I think you have to decide what friendship means to you. Your friend is engaging in a hurtful, self-destructive lifestyle. That’s not good for him or anyone around him. Is this the kind of person you want for a friend – someone who is deceptive and hurtful? Imagine if you were the one that was being cheated on – would you prefer that someone let you know about it? Or would you rather everyone keep quiet about it until you wasted more of your life being involved with someone who doesn’t really care about you after all?

Cheating is painful. It can and has ruined lives. Personally, I wouldn’t consider someone who is cheating to be a real friend. It says a lot about them especially if they expect you to carry that burden with them by remaining quiet.

If it were me, I would strongly encourage my friend to fess up and resolve the situation one way or another. I would give him some time to do it for himself. If he refused then I would have no choice but to disclose the information myself. Does it take courage to do that? Yes, very much so. Will there be a lot of unpleasant consequences? It’s quite probable. But your friend needs to wake up and learn how to treat people right, especially the people that love him. If he gets away with it this time, then he will simply be more emboldened to repeat this kind of behavior. And this kind of behavior is NOT good for him. Over time it will compound and all of it will catch up with him eventually. As a friend, look out for him even when he refuses to look out for himself.

Will you most likely lose a friend by intervening? Yeah, you probably will. But what kind of friend are you really losing? And there is also the possibility that his girlfriend could become a friend that you gain.