[Angrist]

I'd go for "confront Brad and tell him if he doesn't tell her I'm going to tell her", though that might be very hard.

What a sucky situation. Are you sure about it? Isn't the roommate pranking or something? You might want to bring your fists when you tell Brad...

Before I read about the cheating part, I was going to say "you don't want to come between them, it wouldn't help their relationship". How ironic.