Honestly, the fact that we will never have an elf have an extra-marital affair will be a much stronger question that the audience is going to find unusual than lack of queer characters. 'No sex outside of marriage' fits well with Catholic moral teachings, but is hardly the standard in modern American society nor the way sex is portrayed on American TV shows. I am reminded of the scene in
Dances with Wolves, when a very simple wedding ceremony is
still preceded by an 'illicit' night together. As if the idea of having sex after marriage is way too boring to audiences. Elves will already look
very different in this regard. I am totally fine with not even implying that Beren and Lúthien consummate their relationship until
after her father accepts it and they get married. Wandering in the forests alone? No problem, Beren can be a total gentleman about it and the clothes stay on. But audiences are going to wonder about that one, for sure.
I should have mentioned that in the 90's, it was much more common for sci-fi/fantasy shows to use something else as a metaphor for homosexuality than to portray homosexual characters. So, in
Star Trek: The Next Generation, you have a planet where the people (who all seem to wear glasses) reproduce asexually (with pods?) and the woman's interest in Riker is considered to be atypical/wrong in her culture. The show ends with her going through a re-education process and getting in line with her own culture's practices. In the X-Men, you get the mutants experiencing their changes when they hit puberty, and the scene in
X2 where the kid sits his parents down and explains who he is, and they ask, 'Have you tried not being a mutant?' And in
Buffy, you have Willow as a gay character, but there is a heavy 'magic=sex' parallel to how that is introduced...she performs a magic spell with her partner, rather than has a typical bedroom scene to establish the relationship. [Vampirism=sex is obviously common in most shows that have vampires, and some of the earliest vampire stories had lesbian characters, but I don't know if there's a TV show or movie that has done much with that because I haven't watched any of them...I guess Lestat and Louis in [I]Interview with the Vampire?[/I] I prefer vampirism=savage violence stories.] And to go back to
Harry Potter, the curse/disease of lycanthropy creating a social stigma is linked to AIDS, making werewolves in that universe more or less analogous to gay men in some ways (certainly, the fear of having a werewolf teach the children goes in that direction....)
The point is that these stories aren't really about sex, they're about social acceptance (or lack thereof) of deviants/outcasts. The only elf that we are told is sexually deviant is Maeglin, who had an interest in his first cousin (which is considered incest among elves). So...that's the character whose story is about lack of social acceptance and having to keep a hidden/secret desire which comes back to bite him when Sauron and Morgoth figure it out. Lúthien's entire story is the foil between possessive lust and the freedom of love. The Lay of Leithian means 'Release from Bondage,' and while the freedom there is (of course) the freedom to die indeed and leave the circles of the world....there is also a strong implication that freedom comes from loving someone and holding what is best for them as paramount. The characters who react in a negative (possessive) way towards Lúthien are: her father Thingol, who definitely considers himself to own his daughter and control her fate; her friend Daeron, who acts out of jealousy of Beren, but later repents and helps her escape; Celegorm, who finds her beautiful and marriageable and locks her up; Curufin, who sees her as a means to an end; Sauron, who thinks he can dominate her in a fight; and Morgoth, who speaks of crushing her like a flower and slaking his lust with her for his amusement, leaving her free to sing and dance so he can watch her with hooded eyes....yeah, I'll stop right there, but you get the picture.
It's not like Tolkien was against writing stories of lust. But it seems rather clear to me that he wanted to deal with the topic in the least sordid way possible, so that the actual point of the character flaw came through outside of the experience of temptation. Audiences tend to be very sympathetic about characters getting together and having sex because they want to, even if there is some taboo involved. Selling the breach of social contract as a bad thing is usually only possible if you show who is hurt. The movie
Troy (terrible in many ways), does a good job of showing the concept of, dude, you can't just kidnap this married woman because you think she's pretty. That's not love. There are certain deviant behaviors that audiences are always going to be outraged/disgusted by, so stuff like pedophilia or rape is easy to portray negatively or criminally. Certainly, interracial relationships and homosexual relationships in American media were considered very taboo in the past, but that has changed. If the audience shares the sense of outrage/taboo, no explanation is required. If the audience
doesn't share the taboo (in the case of Finwë's second marriage after the death of his wife, for instance), you have to work a lot harder to sell the scandal to the audience.
So, as a 'for instance,' consider the musical
Hamilton. Several extra-marital affairs are part of that story. One is a throwaway line, a joke - Thomas Jefferson returns to Virginia, and in his 'What'd I Miss?' song asks Sally Hemmings to be a dear and open a letter for him. In 'The Story of Tonight (Reprise)' Aaron Burr confesses that the woman he is with is married to a British officer, to which Hamilton replies, 'Oh shit!' So, they both recognize the impropriety of that and how it could get him in trouble, but there's no real judgement against Burr for this. He then has a solo song "Dear Theodosia" where he gets to express his hopes and dreams for the future - he basically justifies what he is doing as saying it's love. Hamilton's own affair is shown onscreen in the song "Say No To This," where he basically admits that he can't help it if a woman throws herself at him, so....guess that's inevitable. BUT, and this is important, when he's later blackmailed by that woman's husband, and decides to defend himself against any suggestion of monetary impropriety by admitting publicly to the affair, you hear his wife's reaction to this. His betrayal of her is made clear (not in having the affair, but in revealing it, but still).
Burr's affair with Theodosia has no clear victim. Her husband is an unnamed enemy soldier, so...who cares? It's easy to be sympathetic to Burr. Hamilton's affair, on the other hand, hurts his wife Eliza who has been introduced as a real character, and causes her sister Angelica to cool in her friendship towards Hamilton. It's more clearly a mistake worthy of condemnation, especially since his handling of the situation is full of self-justification and ignoring how she would be hurt.