IF YOU HAPPEN to see a longtime pal with a woman who’s not his girlfriend (and they’re not in an open relationship), and he asks you not to say anything, it can become a pretty awkward situation—especially ifyour girlfriend and his are friends.

If you’re torn between doing him a solid and following your moral compass, here’s what to do, according to our experts:

Michael Aaron, Ph.D., psychotherapist/sex counselor: Your buddy’s acting in a way that’s very hurtful to his girlfriend. If you help him out, you’re helping him hurt her, so obviously that feels wrong. Listen to your gut and do what feels right, whether that’s avoiding involvement or telling his girlfriend. Either way, stick to your values. Also, what if you don’t say anything, and your girlfriend finds out you knew all along? Won’t she be furious with you?