Leave a letter in her mailbox telling her, obviously without your name on it. But I wouldn't get in that.
Good luck either way.
You know that one of your friends who is married with kids is cheating on his wife. Do you tell her?
Absolutely not.
Honestly, it's their business not yours and it's very sticky territory to traverse. I guess it's equivalent to a cop being called into a domestic dispute. You could be mauled by both parties.
If you tell her about it, and if she reacts, their marriage will probably end.
If you do nothing, she may not find out. The affair may end (as affairs usually do) and they may continue to live together happily. Or she may find out on her own and take whatever action she deems fit.
By telling her you can only provoke a confrontation and the outcome isn't likely to be a happy one -- for them or for you.
Dangerous territory, if you tell, you'd better be 100% about it and have the proof to back it up. Otherwise you'll lose a friend.
My ex cheated on me and I would have liked to have known long before I found out. I wish someone had told me!
