Is it fine to disclose an affair.

If his wife suspects that he is cheating and has not aken any action she may not want to confront him about the situation. She may be afraid to lose him. If the husband denies it an she must choose between the two of you, what wil happen between all of you as far as your friendships and relationships? I think that you should still tell her. I just would be aware of the possible consequences. It may be helpful to her if you have some type of proof to offer.

I understand your dilemma. The wife will greatly appreciate you for telling her, but your friend may not forgive you. If I were you, I would speak to my friend first. It might be more convenient for him to be truthful and deal with the problem amicably with his wife. Sometimes, hearing from a 3rd party is more hurting.