In-game, sex rarely comes up so in-game sexuality rarely comes up either. Occasionally, players will, in-character, ask about the attractiveness of NPCs or utilize their own in a manner when being charming or diplomatic, which is fine. But as far as exploring sexuality further than that at the game table, I don't keep exploration charts on hand for such things. I've got no problem with someone playing heterosexual, gay, or bisexual characters but it's unlikely to come up much in-game, maybe not at all.
When running games at gamedays or conventions (particularly for younger players), such matters (and details of graphic violence) are strictly forbidden. I've even taken one adult player aside at a convention and asked them to clam up or leave the game when she felt compelled to make her character overtly sexual (Living Greyhawk game - player character in a cat suit, with whips for weapons, constantly propositioning other player characters and being extremely suggestive with every sentence). I don't care to run such games, so I don't, and I wouldn't play in them either.