I would leave. He's either already, or in the process of turning gay. Probably ashamed of it, hence why he hides it so much, and may be why he keeps a girlfriend. To give him the ultimate cover up. I have a friend who is gay and all through junior high / high school he always had a lot of girlfriend but we all could tell he was startin to turn.

Anyways, yeah that's really gross. I would leave him.