Good Luck, Peter. I have two daughters in their early twenties who both live at home. We have basic rules that are respected and these rules apply both ways, for example a reasonable expectation of privacy, and a respect for my feelings. These include time when they can watch a movie in a room by themselves, albeit with an open door, and the bedrooms are always off limits. The girls travel with their boyfriends, and sleep there too from time to time. This might be the way you choose to go with your son.
My sister is gay, and happy, in a long term committed relationship with someone who respects her. What more could a parent ask for?
Another note, gay is not a lifestyle choice any more than heterosexuality is. Did any guy ever choose to be attracted to girls? Of course not. Your sexuality is part of you, and cannot be changed or prayed away, just accepted.
Lew, very well put. Thanks for your insight too.