I've had a few gay NPCs in my various campaigns, but as others have said, the topic rarely came up, so I don't think my players were particularly aware of most of them.
In the game I'm running now, however, one of my players is playing a gay character, and he actually worked the orientation thing into his backstory.
In brief, he began the campaign as a fallen paladin, though the rest of the party thought him just a fighter/barbarian. He had been excommunicated from his Church when his orientation was exposed, and had lost his powers because he felt his god had abandoned him. In a recent game, when he actually came face to face with an angel who told him, in so many words, that it was only the mortals of the Church who had turned their backs on him, and his god never had, he found his faith and his powers restored.
I'm not sure the brief summary is doing it justice, but it was really a great scene to play through, especially since none of the other characters (or players) had any idea all this had happened until they witnessed the conversation with the angel.