[ninjagirl93]

You should talk to him.. tell him that he should come clean. Tell it from the perspective of a girl who has been cheated on. If he cares about you (and her), he'll understand how truly horrible it can be and out of respect for you (if nothing else), he will tell her. If he doesn't want to then you have to weigh out what you value more: his friendship or your personal reasons (i.e. telling her out of principal bc of what you yourself faced etc.). I've had some guy friends cheat but I've never told their girlfriends, mostly bc I was not friends with them, and my loyalty lay with my guy friends. That does not suggest that cheating is okay but I just figure its not my place. Also, would it really be worth it to lose his friendship? His girlfriend might not believe you, and it could cause a whole lot of drama.