My novel contains a F/F couple, though if we must split hairs, if you asked each, point black, about their sexuality, one would identify as bisexual, while the other is a proud lesbian. When I originally was crafting the characters and their relationship, I originally saw it as being one-sided with one character taking advantage of the other's feelings in order to get her to do stuff for her, but at some point, between the thinking and the typing, I ended up completely rewriting it. The girl (the bisexual one) eventually became more of a heroic character, who is genuinely in love with the other girl. It's probably for the best: I've heard so many complaints about the Depraved Bisexual trope. It's probably best to avoid that kettle of fish, so to speak.
Generally though, in my story, no one really raises an eyebrow about their relationship. Both because it's set in an undetermined point in the future and because it's a post-apocalyptic story. My general belief is that society is moving to the point where, whether you like it or not, gay couples will generally be accepted. I see at as being similar to the interracial relationship debate. Until Loving v. Virginia struck down laws against such relationships, the bigots used many of the same arguments against those relationships that the bigots of today use against gay marriage. That it's unnatural and if we let black people and white people marry each other, who knows what will happen, and all that BS. I'm not saying interracial couples don't still face difficulties, but as a general view, only the most lunatic of fringes goes around ranting and railing about how they shouldn't be allowed to marry. That's what I see happening with the gay marriage issue.
Also, in a post-apocalyptic setting, people are generally more concern with staying alive than with someone else's sex life. So no one really cares if said character is gay or straight or bi, so long as their love life doesn't affect them. There are bigger things to worry about.
But I freely admit that I wouldn't be comfortable writing sex scenes with my characters, but in general, I'd be squeamish about writing erotica about straight characters as well. Really, the most my characters do is kiss. To paraphrase George RR Martin, I am a typical American in that I am more comfortable writing about an axe sliding into someone's skull than a penis sliding into someone's vagina. I'm not going to say I'll never write sex scenes, because life has taught me that God loves nothing more than upsetting never statements, but right now, it seems unlikely.