>>5 Dude, this is not yaoi. If you read the comment its yuri or lesbian.
I'm a bi, so I understand the struggle of having the same sex relationship. I suggest that if you value your friendship and want to stay friends with that guy, both of you have to confront him and tell him the truth. The longer you wait the more painful it gets. Tell him before he ends up hopelessly in love with her. Just make sure that he knows how to keep a secret.