I think that it is easy to fall for a same sex friend when you're also attracted to the same sex. But I think it is also more difficult for a straight male friend to handle the news well than it is for a straight female. In general of course.
Maybe we shouldn't worry about labels. Gay, straight, bi, whatever. In the moment of things we don't always act like we normally do. If it felt good, and it probably did. A bj, is a bj. But key is don't feel guilty. If it does bother you, then don't drink so much.
He might be gay or might now. I think the fact he knows your bf and guys don't see each other like hard and stuff, it just might have been hot. Weird but I don't think it mean he's gay but maybe just horny.