I know a guy friend who has cheated on his spouse. They have since cut ties, but I do not think his spouse knows what happen and I feel awkward being around them now. The friend does not know I know about them being unfaithful. I now question my own relationship with the friend since that behavior does not go along with my own morals or ideals of a happy marriage. Part of me wants to tell the spouse what happened, but I am afraid of the backlash from mutual friends and I do not see it as my place. They no longer talk as far as I know and it was not sex, just a kiss, probably drunk when it happened and some phone calls after which have all stop. I feel that many people know but the spouse and I would hate to be in that person's shoes and finding out later how many people knew but me. If no one ever tells and my friend is not truthful then its a little dirty secret that a lot of people know about.
-Bearer of Bad News
What a difficult situation to be in. Ideally, you would just be able to say, "This is none of my business," and let your friend tell his spouse and deal with the fall-out. But unfortunately, the friend is not 'fessing up. I agree with you - if I were the spouse, I would want to know what happened. It would feel foolish to find out, years after the fact, that many people knew my husband's indiscretion, but I didn't.
First, I must clarify - you must only consider telling if you are absolutely sure this man cheated on his wife. If this is a rumor, then please ignore it. But if the friend confessed to you, or you saw something, then you have good grounds for sharing the information with his wife.
I would recommend giving the friend a chance to confess first. Tell him that you are concerned for his wife, and that if he does not tell her within 3 (or however many) days, you will be sending her a letter/email with the details of what happened. In the letter, be brief and stick to the facts of what you know. Bear in mind, doing this will likely ruin your relationship with this man and his wife. You will likely never be on friendly terms again. But, I think it is more important to help this woman than to maintain a friendship.
Thank you for writing,