It seems an interesting thing to want to explore at the table, but perhaps it needs a very select group. In the world I play in, homosexuality is just as acceptable as any other for the most part and nobody cares
In my Greyhawk campaign world (world because it's two campaigns in the same setting), homosexual NPC's certainly exist and are the PC's are occasionally aware of one (like through Detect Thoughts on an NPC), but they are not particularly open about it.
For example, the rulers of Hommlett, two former adventuring buddies who live in a tower together and rule together, are gay, in "original" Greyhawk per Gygax and in my campaign because I like that. I never realized it when I played that adventure, but in a question on ENWorld about gay characters, Gygax pointed to that and said it was "obvious" they were gay.
In my real life, growing up in a small town in the 1970s and 1980s, I didn't think much about the possibility that people were actually gay until I got to college and first met people who were open about it. Like in my hometown, the two old ladies who lived together and ran a farm where we used to buy eggs -- thought never crossed my mind, though it was obvious to my parents.
So I figure my campaign world is like that. Not something that has dread implications if revealed, but not something people are typically open about either. So a gay character might be open about having a roommate who is a close friend, but probably wouldn't refer to them as a significant other, at least not around people he didn't know.
Which fits well for the campaign I play in (but don't DM) too, where one of the players is (I suspect) in the closet with us -- he was in the military, so if he is gay, he's probably quite used to avoiding the topic. When my wife met him once, she was sure of her gaydar, whereas had only a vague idea that he never talked about women, in character or out.
