WQ: I happened to find out from a very reliable source that my friend’s boyfriend is cheating on her. I feel weird knowing something that she doesn’t, and I worry that she is going to be badly hurt. Should I tell her?

A: There’s no easy answer here. When you tell a friend that her partner is cheating — and your proof had better be irrefutable — you are risking two likely consequences: 1) the end of your relationship with the person whose behavior you are exposing, and 2) the end of your relationship with your friend.

The reason for the first consequence is obvious; the reasons for the second, less so. What if you do tell your friend what you know about her unfaithful partner? Say she confronts him, he denies it, then manages to convince her that you’re nuts. Guess how she’ll feel about you then? Or, even if your information does lead this couple to break up, if they get back together, guess who they won’t want around anymore? There’s a good chance that the cheater will never want to hear your name again — or that, no matter how good your intentions, your wronged friend will decide that you tried to break up her romance.

There’s also the possibility that despite the infidelity, your friend’s relationship may not be wholly bad. Other than the matter of this guy’s infidelity, this couple might be doing very well, thank you very much — and your revelation could change all that. Though ending the relationship may be the morally justified thing to do (in your opinion), it may not be the best thing for these two. Do you want to have that responsibility on your head?

What you have to realize is that if you act like a good Samaritan and give your friend information you’d want if you were in her position, you need to be prepared to bear the brunt of her unhappiness and frustration. Ultimately, she may blame you more than she does her straying guy. That’s why revealing what you know may not be worth it.

On the other hand, you may feel that this is one secret you can’t keep, especially if you believe that your friend’s continued involvement with this man will threaten her future happiness. In that case, you may want to approach Guilty Guy and tell him what you know. Don’t threaten him; just explain that this knowledge is weighing on your mind and that you hate the idea of his partner being heartbroken. He will probably be shocked and dismayed by your directness, but at least he can’t accuse you of meddling. The burden will be on him to search his heart and do the right thing (such as stop cheating) if he wants their relationship to continue. And you’ll know that you’ve done what you can.

There’s another, less direct tactic you may want to consider: One night when you’re out with your girlfriend alone, bounce some hypothetical questions off her (without being too obvious). Ask, What would you do if you knew my boyfriend was cheating on me? or, Would you want to know if there was something going on behind your back? Consider her answers and act accordingly; you may be surprised to find that she thinks ignorance is bliss — many women do.

The bottom line? No matter what you do, the outcome may be painful, so think long and hard about your course of action.