If you've fooled (not sex) around with a friend's husband or wife, but you know it was a mistake, is there any reason to tell the friend? How does one make amends? I am deeply sorry, but do not want to make matters worse.

You know, you may not believe it but I am going to say do *not* tell the friend.

I say that because 1. it won't change what happened, 2. it won't improve your relationship (and probably end it), 3. it will (further) damage the relationship with her husband.

You probably need to back off from being around them both, though until you can cool off.
In the past, I never told on friends who were being unfaithful unless one of two things happened:
1. the significant other asked me directly, in which case I wouldn't like, or 2. my friend was cheating constantly and showed no sign of caring or stopping.

Assuming it was a one time mistake, put it behind you. If it's a pattern of behavior, point it out but be prepared to lose your friend in the bargain (I did...twice).

Ask me anything