The first thing to keep in mind is that most of the major human reasons for "random pairings" are simply not operative for Elves, of either gender.

            1) I'm bored and I can't think of anything else to do.

            2) I need the illusion that I am understood and loved.

            3) I need to breed/screw. Those old biological imperatives, you know.

            4) I get lonely by myself because I am a boring person and would rather be miserable,
             and making someone else miserable, than alone.

            5) I am truly pathetic and have no real personality, so without the affirmation of someone
                pursuing me, I feel worthless.

            6) I need stuff and a relationship with a well-heeled individual is a good and traditional
                way to get it. Equally applicable to either gender, btw, historically. (Domestic services
                count as stuff, in this case.)

            7) Again, I am a boring person and I need to get high on endorphins so I don't have to
                deal with reality. (Yes, there is a certain amount of repetition.)

All of these -- which seem to be at the bottom of 95% of the Truly Miserable Relationships which  I have been witness to over the years, in more detail than I ever wished to know¹ — are nonexistent for someone who is an immortal telepathic genius-polymath with such sensitive perceptions that starlight is the equivalent of a natural high. (I will not insult teenagers by saying "They're not teenagers, they are wise immortals after all" — because such shallow and manipulative and self-absorbed behavior is, alas, typical of humans this side of the Sundering Sea from adolescence to the grave — and generous wisdom, though far rarer, may also be found in mortals of any age, or Age.)

So that leaves us with True Love, (aka Soul Mates) on the Good side, and Obsessive Stalker Behavior (aka Controlling Lust) on the Bad side. Very different dynamics. And not a lot of people historically on Side 2, most of them being in the category of "How Many Times Did He Bounce On The Way Down?" ²
 

Reasons why you should NOT write a romance

If in all honesty you must admit that any of these statements apply to you, put down your fanfiction and rethink your world-outlook before you resume it:

            1) I cannot write emotional intensity — so I substitute sex scenes and/or boilerplate bathos
                from stock footage of TV romances, however inappropriate or implausible in context.

            2) I cannot imagine any relationship that does not have a sexually-predatory component,
                particularly between visually attractive persons. There is no such thing as friendship in my
                world-view.

And for slash — meaning in this case homosexual non-canonical relationships specifically, not non-canonical relationships of every sort:

            3) I cannot conceive of the word "love" not meaning sexual activity, exclusively.

            4) I have no good male-female relationship behavior models.

I'm somewhat surprised, but not really — that is, I'm surprised to see it being admitted, because it's the kind of thing I have often been tempted to suspect — when someone writes in an A/N that they're writing slash because m/f relationships are inevitably about domination/submission, or as the song goes, "Some people want to abuse you/Some people want to be abused/Sweet dreams are made of these/Who am I to disagree?" (Inevitably in the sense of philosophical necessity, too, that being the way that things are meant to happen — not in the sense that "Everything in the world is broken from the start, so of course every relationship is going to be Marred to a greater or lesser degree.")

"I have no good behavior models" should be a tip-off there, that maybe you aren't going to be able to write a good homosexual relationship either. (And anyone who thinks dysfunctional homosexual relationships are somehow more "romantic" than het ones needs to read Greg Louganis' autobiography, talk to someone who's been in one, or excercise a little imagination.)

If you haven't the foggiest what a functional relationship would look like, then perhaps you shouldn't be trying to write a romance at all yet — at least not as a finished work of art. As an excercise in trying to figure out what one would look like, it can be quite helpful, but then it is really a tool for philosophical investigation. The results of it, once incorporated into your own thought, may well then become the foundation for writing plausible romances.
 

Learning what love looks like

How shall you research this? The most obvious answers are the least practical. Going out and engaging in romantic relationships without any clear philosophical understanding of the various things called "love" is perhaps the least helpful of all of them. Watching real-life interactions of others is a little better, since it removes one of the most confusing of all elements, the involvment of self, with all attendant conflicts and deceptions — but that too is less than helpful unless one has a great deal of understanding of principles already, and great perception, to sort out the morass of other influences and interactions which have nothing to do with anything remotely resembling love, but which are simply entangled through every interpersonal relationship, familial or otherwise.

One thing I can tell you, from personal and secondary experience, is that being stalked, menaced, emotionally blackmailed, yanked around by the erratic and emotionally-unavailable, and otherwise controlled is not fun. This sounds incredibly silly, to state this — but it seems to be necessary, based on the number of fanfictions, author's notes, and reviews in which the converse assumptions are revealed to be held. These are the stories in which a character established in the canon as virtuous and compassionate (like Aragorn or Haldir) is turned into a brutal rapist or a whining, deceitful manipulator, and this is hailed as such a "romantic!" envisioning. Or where a canon character who suffers from the unwanted attentions of a violent control freak is castigated as "such a bitch!" and expressions of hatred heaped on her by writers and readers alike. (Sword-swinging precog and faithful rebel Idril comes in for this a lot, for daring to prefer the gentle-spirited nature-lover Tuor to her acquisitive, ambitious and ultimately treacherous cousin Maeglin, the darling of "bad-boy" worshippers. I certainly hope and trust that these commentators are not speaking from personal experience of having been stalked and menaced by an unencouraged admirer, but only from ignorance and naiveté, as the former would indicate a level of psychological damage and brainwashing almost beyond belief.)

Real life is not a controlled situation, nor is it a fit place for experiments in the field — the stakes are too high, the factors too many, and not to be easily disentangled. What we can at least do is consider relationships abstractly, and in case histories: is this a reasonable respose for these folks, given their backgrounds? What are their backgrounds, anyway? Which brings us to what is known about the social behaviour of the Elves, apart from the glimpses we see of it in The Hobbit and LOTR, and the broader examples in The Silmarillion, which are however simply chronicled, as if told within that foreign Elven culture, and making assumptions which are not obvious to us as outsiders.  This is a little known, less-understood document entitled "Laws and Customs," which in its several versions was part of the background working-out of the details which Tolkien engaged in to shade in and give weight to the world of Middle-earth, found to date only in the hardcover volume of the History of Middle Earth entitled Morgoth's Ring. And does it ever tell us a lot — about ourselves as well, for finding it strange and disturbing, too.
 

No Harems in Aman

Equality of the sexes is an Elvish given. This ought to be implicitly clear to everyone who gets as far as finishing FOTR: there's no question that Galadriel is the one in charge of Lothlorien, and that everyone there thinks that's how it ought to be, and outsiders consider her advice and assistance to be worthwhile — even divine Immortals on errantry. After all, maintaining centuries of 24/7 resistance to the most powerful Dark Entity on Arda while simultaneously running a small nation isn't something that just any Joe off the street could manage. It's very funny to me (in a macabre way) that so many female readers are so unfamiliar with even the idea of a powerful, competent, independent-minded woman in charge of everything, that they can't begin to wrap their minds around it and have to warp her into an evil psychopath to ground themselves — instead of looking at her as a role model, and her assertive-yet-respectful relationship with her equally-heroic (if less "powerful") husband as something to be emulated.

According to "Laws & Customs," there are some gender differences to be seen, in that invention the development of new things seems to tend to take the form of having children for women, — that is, childbirth and childrearing are equated with invention, discovery and the arts and sciences. But this is neither absolute nor permanent — it certainly doesn't mean that Elf-women are ghettoized as hausfrauen with a spurious honour paid to them as "pillars of the home," to keep them content — because as immortals the "Years of Children" are brief (comparatively, that is, frex, there's about a 60 year span (or possibly longer, given the calendar complexity) between Galadriel and her oldest sibling, which means that even in a family of five there are never any times when the house is overrun with screaming children) — and then parents move on to do other things that interest them:

        "But they have many other powers of body and mind which their nature urges them to fulfull. Thus, although
        the wedded remain so forever they do not necessarily dwell or house together at all times…"

And none of these talents are limited to one gender or the other, though some attract more men than women, and vice versa:

        "There are however no matters which among the elder only a nér [male] can think or do, or others with which
        only a nis [female] is concerned."

Even though for reasons of local custom as well as personal inclination, broadly speaking, Elf-women tend to favour healing, farming, musical performance, fiber arts, history, geneology, and lore, while the Elf-men favour cooking, smithing, building, carving, composition of music and poetry, and exploring, none of these divisions are absolute or culturally mandated in any way — nor are any others:

        "But all these things, and other matters of labor and play, or of deeper knowledge concerning being and the
        life of the World, may at different times be practiced by any among the Noldor, be they néri or nissi."

A female smith-explorer-sculptress-inventor-philosopher might be somewhat unusual — but far from unheard of: this is in fact the exact description of Nerdanel, the wife of Feanor, who met her future husband on one of her wide-ranging expeditions and was famous for (among other things) devising strange but wonderful abstract artworks out of her own imagination. "Renaissance women" are the norm, not the exception, among immortals.

Even female pre-eminence in healing, which seems to fall into a "traditional" (for us) division, with the belief that women are necessarily better at nuturing, doesn't according to Elven sages come from a gender-based ability, but from the tendency of more men to be attracted to hunting than women, and their belief that killing things (even perfectly legitimately, for food or defense) crippled that talent, (though not, it would seem, permanently) "and that the virtue of the nissi in this regard was due rather to their abstaining from hunting or war than to any special power that went with their womanhood. On the other hand many Elven-men were great healers and skilled in the lore of the body." It is impossible to forget that Elrond, a former war-leader, is in the Third Age reknowned as a master healer. And again, on the other hand, it is stated that in times of  necessity Elven-women fought in defense, and compared to mortals there is far less physical difference of strength between the sexes.

In brief, sex is fun, something in which they take "great delight" and a part of their lives that the Elves think very highly of, but they're not controlled by it, and it's kind of like a hobby that they usually do for a phase of their lives and then move on to other things after they've explored it fully.  Bearing and begetting children is completely voluntary, because due to their perfect mind-body integration, "with regard to generation the power and the will are not among the Eldar distinguishable." Romantic love isn't something intrinsically different from friendship for them except that it's closer and more lasting (usually). They bond for life, and only with one soul-mate, "and they never had need of any law to teach this or enforce it" — but it doesn't look much like "conventional" marriage to us, since both spouses have their own careers (plural) and as time doesn't have the same meaning for them as it does for us, they can be quite happily apart from each other for years without this indicating that there's any "problem" in the relationship.

In fact, the formal celebrations and legal aspects which we think of as constituting marriage are completely irrelevant to the Eldar: they like having the parties, and the presents, and giving each other jewelry they've made (as well as spouses exchanging rings, the parents of bride and groom give their new son and daughter ornaments, which as Christopher Tolkien points out casts a new light on foresighted Galadriel giving Aragorn a gem in Lórien)-- but none of this is necessary, though it's considered civilized behaviour. What makes the marriage is the personal promise and the physical consummation, not the societal aspects. And they don't rape, or the euphemism beloved of the authors of bodice-rippers, "forced seduction" — "for this was wholly against their nature."

With regard to harems — the only time in which the question of multiple partners came up in history was a highly anomalous situation, in which one of the three original Elf-kings loses his wife to post-partum depression, and since she never wishes to return to the land of the living, and he's lonely, and has found someone else, he appeals to the gods for the right to remarry. This messy romantic situation resulted in bloody dynastic wars and vastly complicated the fight against the Dark Lord down the line, and "the sorrow and strife of the House of Finwë is graven in the memory of the Eldar" — meaning it isn't something they take lightly. But one upshot of the long Valinorean discussions about the problem was the definitive statement on polygamy:

    "By the law of the nature of the Elves, the néri and the nissi being equal, there can be union only of one with one."

This declaration is made by no less than Namo Mandos — the Judge of Right and Wrong and the speaker for the Dead of Arda on behalf of Finwës dead wife, who doesn't want to be forced to come back to life (even though there is no issue over risk of future childbirth, since conception is biologically voluntary for them) and whose personal decision though considered regrettable, has been upheld.  There's no question of one male "owning" multiple females, as if they were all animals, far less that women were "property." (This is a radical break from most ancient human philosophers of this world, even St. Augustine, who all seem to think that the servility of women to men and the "ownership" of a plurality of mates is part of the proper order of things.)³
 

What this means for the fanwriter — lots

First of all, no arranged marriages or otherwise forced marriages for the Eldar. This is just common sense, quite apart from the value placed on individual freedom and mutual respect. The socio-economic ones aren't valid — because Elves are immortal (for a given value of immortal⁴) they aren't affected by the human concerns of consolidating property for their heirs, forging political alliances by this means, or dumping their extraneous offspring on someone else to support.  The few anomalous instances of parental or other coercion in romantic matters (positive or negative) are chronicled as Great Mistakes in Middle-earth History, not everyday behavior.

No Elven daughters told they can't travel, can't do anything 'unladylike' or must remain dutifully submissive and meek — and thus, alas, no Spunky Young Women defiantly running off to become warriors, either. (And no Elven men scornfully remarking on how cooking, sewing, or helping raise the children is "women's work." The only thing anyone is actually limited from doing is making lembas — that secret is women's alone, taught to them first by the Valier Yavanna.) It's all a matter of individual preference — even if more Elf-men than women typically do want to go out hunting, no one is going to stop Beldis from joining Beleg in archery, or tell the latter that it's "unmanly" to fix the dinner afterwards! ⁵

No Elven rapists. Or child-abusers. Any effort to control (much less torture) the spirit, or the body, of another, of whatever sex, race, or state of being (i.e., living or dead) is said to be of the Dark Side. Anyone who does these things or wishes to do them is far under the influence of the bad guys, and not just in a hapless, involuntary, I'm-a-prisoner way: the rare examples in Silm. are all (and this is true of Elves and mortals) of those individuals who have made a series of deliberate life-choices to indulge in violence, aggression, greed, disrespect, or other controlling behaviours towards their fellow sentients. There is, in fact, a somewhat ambigious statement in "Laws & Customs" which speaks of raped Elves reatreating into death from such abuse, and while it is not clear (i.e., could be interpreted either way) if it only means married Elves, who are thus forced into a sort of involuntary bigamy, or all Elves, by virtue of the cruelty and injustice of the act, it is not a gender-specific statement.

No prudery. Since the Elves have no need to be worried about genetic purity (which is basically what all the worry about female sexuality and "disgracing one's family" comes down to, along with economic issues) and aren't either at the mercy of their physical impulses or from a culture which believes that unprotected women are the legitimate prey of males, there's no reason in peacetime in secure areas (such as Aman, or within Doriath, or along the seacoast of Beleriand during the Long Peace) for Elven-women to be restricted from going anywhere, with whomever they please, at whatever time of the day or night. Curfews on Elf-maidens? —Lúthien's parents don't even notice that she's spending most of her time with Beren out in the woods of Doriath, until Daeron reveals it. (This also explains to an extent the disaster of Aredhel, who being used to this, finds it impossible to deal with any limitations on her travel whatsoever, in the more dangerous climate of the Old World, and falls foul of that aforementioned Darkside corruption of both nature and other Eldar.)

No languid, helpless, "ladies of leisure." Not even among the highest Elven nobility. Indis, Finwe's second wife, and Galadriel's paternal grandmother, didn't make things with her hands, but this is because she was Vanyar, not Noldor, and the Vanyar weren't really interested in material possessions: they were mystics and in Arda this means musicians — which Indis was. She was however also "exceedingly swift of foot," which isn't something anyone would know if she didn't run around plenty, and full of bubbly social energy — "there was ever light and mirth about her while the bliss of Aman endured" — in other words, a people person, and quite athletic, along with being a talented vocalist and performer.

No "girly" males. (No use of "girly" or other terms pertaining to the female sex as insults, either.) If you're going to write slash, (and I'm just not bothering with the semantic questions of the politics of the word "slash", just as here I'm not bothering with the question of whether or not it's necessarily AU,⁶ I'm just using it as it's commonly understood for convenience sake), you have no warrant for making either partner a stereotype, "seme" or "uke," with the usual jargon that "one of them is 'the woman' in the relationship." After all, since Elven women can do, or be, anything, (as can men) — what exactly would that expression mean?
 

Conclusion

So, where does this leave the would-be romance writer? With a lot of trite, much-trodden avenues closed off — and a vast uncharted territory to explore. What would a courtship look like, shorn entirely of any uncomfortable feeling that love is "mushy stuff" unworthy of males, or that "being together" is necessary because "that's what everyone does" — and of any sense that the female "ought" to be the subordinate partner, never seeking to excel or in any way "threaten" the insecure, "dominant" male by competence or independence? Where it's expected that each person will have their own individual lives, interests, projects and spend personal time engaged in such pursuits alone? And that both spouses will contribute equally to the care of any children in a marriage? Scary stuff, this egalitarianism of the Elves — and exciting. It's already being explored in the worlds of futuristic sf — so why not take advantage of a world already built for us where it's the norm, not the hard-won exception? Be daring. Write a real Arda romance!
 

Afternote: A little bit about Biology, aka, Snot is also a four-letter word

It is unfortunately not possible to write a serious essay on writing romance without addressing, however briefly, the problems of writing about copulation as well; but this section (though not terribly detailed) may be skipped by those whose consciences require it and who do not intend to go beyond the traditional fade-to-black of noir films. However, anyone who intends to write about the physical aspects needs to bear a few things in mind, points which seem to be largely unknown in the world of fanfiction (regardless of fandom or genre) but which are important for writing sense of moving sensuality, rather than accidental farce.

No self-animating mammaries. Normal female breasts do not contain muscles, tendons, ligaments, air bladders or other structures which would allow them to spontaneously swell, bob, pulse, bounce, expand or otherwise maneuver without exterior pressure, and only a very small amount of erectile tissue. (They're mostly fat, in fact.) When at rest (i.e., standing still, or lying down) the only natural motion will come from the inflation of the underlying ribcage, yielding a rise and fall slow or rapid depending on respiration rate, but not a sort of random bobbling like that of a pool-float. Other movements, such as arm extensions, will cause a shift due to the underlying motion of the pectoral muscles. Otherwise they don't move any more than earlobes do, by themselves. I know that this will come as a shock to some writers (particularly in other fandoms, such as Xena) but this is just basic anatomy & physiology, really. What surprises me is that it is apparently foreign information to authors who presumably have these organs themselves.

Mucus membranes produce mucus. Not nectar, ambrosia, honey, or other vegetable derivatives. (Unless your characters are Bee Women From Mars or the like.) And mucus, aka phlegm, is also known less politely but no less familiarly as snot.

Touch does not equal pleasure. For either gender. (If you don't believe this, you've obviously never had a medical exam.) Voluntary sexual encounters among humans often being somewhat lackluster in the pleasure department (hence the long-standing trade in enhancements) you will not find "pleasurable" rapes occurring outside the pages of bodice-rippers — whose narrative is so far removed from reality, or research, on every level that they cannot be considered authoritative. On the rare occasions when a rape triggers an ejaculatory reaction, (more common than in women, who often don't attain orgasm even in voluntary, desired sex) this is no more indicative of enjoyment than it is of consent: it is as involuntary as a gag-reflex causing vomiting (something far more likely to follow a rape, from the crime reports and personal accounts I've read.) So this way of getting around the rape-entailing-death of L&C (as I've encountered) just doesn't wash.

Lavender is an antiseptic. (Hence its kinship with the words "laundry" and "lavatory.") And antiseptics don't feel good on mucus membranes, to put it mildly. Most essential oils, in fact, are somewhat pungent, and just because they smell nice doesn't mean a thing. Hint: if you wouldn't want something splashed in your eyes, you probably don't want it in equally-sensitive locations.

Peritonitis. Look it up, before you subject your characters to extremely-violent sexual abuse. Even with superior healing abilities, it isn't something you just bounce back from. (Without them, and without antibiotics — you're dead. Slowly and painfully.)

² Some examples: Eöl used magical subterfuge to make himself look like Aredhel's rescuer/refuge, thereby behaving in a coercive way, though much subtler than any "forced marriage" or rape. His possessive attitudes towards spouse and child eventually resulted in him being thrown off a cliff for killing his wife when she tried to take their kid and leave him. Maeglin, their son, intended to kill his rival, his rival's son, and take his wife by force, and got thrown off the same cliff, proving again that being a control freak is a recessive behaviour. Would-be (and undoubtedly former) mortal rapist Forweg only had his head bounce — separately.

³ There are people who have read "Laws & Customs" and still insist that Tolkien was a benighted misogynist. I can only conclude that they are slightly out of phase with the rest of us, and inhabit a dimension where everything is backwards, but are nearly enough in synch with this dimension to interact with it — I certainly can't come up with a more logical explanation. The fact that L&C declares that the keeping of history, genealogy and lore was particularly a female-dominated hobby is especially telling.

⁴ Immortality, for Elves, is according to their most common beliefs, only for as long as the world exists. Mortals however, die from this world, but leave Arda for eternity beyond the Walls of the World, joining with the Ainur. This division of destinies is the core of the tragedy of mortal-immortal relationships. (There are a few dissenting speculators, however, who talk of a Second Music in which the Children of Eru will help create a new world after the Apocalypse.)

⁵ Beldis is a real name, and of Elven form, though the instance where it is used in the HOME genealogies is of an Edain woman — but many of the Edain names are actually also those of real Elven characters, (like Gildor, Mablung) so there could very well be an Elf-woman named Beldis in Arda as well. (It means "mighty" + "woman", btw — that is, it's just a feminine form of Beleg.)

⁶ MPREG, or Male Pregnancy, is however automatically AU, at least in this fandom. There just isn't that kind of "magic" going on in Middle-earth the way it's used to rationalize it in the stories I've read. (The ones that bother to try to explain it, and don't say, "LOTR is fantasy, so anything can happen." Yes, I've read that.) It doesn't have to be so in all universes: professional sff author Martha Wells has written a plausible MPREG setup in a futuristic alternate world, but there it's the result of plausible bioengineering, not magic, and the logistics are thought through pretty carefully, based on existing natural models.