If your goal is to still try and save your marriage, then yes -- I think you should confront and expose, and begin to work at healing your marriage with everything you've got. If your marriage is over, then I would go by a favorite quote of mine:
"You always have to tell the truth; I just wouldn't go around tellin' it." If I was asked by a friend or family member, I would tell them honestly "she was having an affair, I'm sorry to have to tell you." If you're asked by an acquaintance, I would keep it to yourself. If you're not asked at all, I wouldn't offer.
"Never shield an infidel from the consequences of their infidelity."
