As a note on sexuality and relationships in game affecting game play. I've seen two cases where the relationships of PCs directly affected the games and how they were played out.

In the Age of Worms game that I DM on of my players had a background where he liked to frequent the local brothel. I wrote in that he managed to get on of the girls pregnant and this led to a much tighter feel for the game as he began efforts to look after her and the child. It got even more tense when the child and mother where later abducted in order to lure the PCs into a trap.

In the crimson tide game in which I play, another party member fell for the charms of one of the NPC's who is now accompanying us through the jungles of the Isle of Dread. He and the entire party are much more intereseted in keeping this NPC alive as a consequence.

Both are perfect cases where "Sex" led to situations both for roleplay and conflict. None of the sex was played out but the relationships as a consequence were definitely instrumental in the game play.

I see no good reason why these forms of social interactions should not be catered for in both hetersexual and homosexual relationships. It only makes for better plot motivation in some circumstances.