dorm etiquette: bringing a girl back to your room

[1aguilas]

I'm pretty good friends with my college roommate and he's a really nice guy, but I feel weird asking him to leave if I'm trying to bring a girl back to our dorm room. He has a girlfriend back home who is not going to visit, so it's not like I can tell him "if you leave the room tonight I'll leave the room whenever you bring a girl to the room". What's my play?