I would confront the husband, moreso to see his reaction to your discovery and his response than any real chance of finding out the whole truth. There's a small chance he might decide to confess. He more likely will take the more travelled route by becoming angry, denying an affair or anything beyond flirtation, even projecting upon you by accusing you of snooping, cheating, being emotionally/sexually distant. Lame excuses may abound as to how this woman is obsessed with him, sends him photos/emails unsolicited by him. Call out his BS. He may storm out or use the silence tactic.
Basically, the confrontation is for you to make a decision for YOUR future. If you decide to end this marriage, I would contact an attorney and discuss your financial situation, child support/custody before notifying your spouse. Be legally prepared and financially aware when you toss his butt out--let him be unpleasantly suprised for a change.
If you really want to try to save your marriage----is your husband willing to be honest about the affair, accept responsibility and the fact that he has erroded the trust and must work with you to fix it, and end all contact with this person? Is he willing to go to marital counselling with you? If he fails to do these things and keeps lying about the affair, it should be seen as the definitive dealbreaker.
"Many angry women and many sanctimonious men heap abuse on women who stand by their adulterous husbands. But if these women and men were to think more rationally and with more decency, they would either keep their opinions to themselves or just wish struggling couples well.
". . . [G]iven the superficial nature of men's sex drive, the sex act for almost any man can be utterly devoid of any human, emotional, intellectual or romantic meaning.
"That is why a wife can understand -- not excuse, but understand -- that her husband can be a good man and slip up. Saints never weaken, men sometimes do. That is why some men who love their wives with all their hearts, who devote their lives to responsibly taking care of a wife and family for years, can without thinking (not to mention without love or a desire to hurt their wife) have sex with another woman one night.
"A woman who leaves her marriage solely because her husband was sexually unfaithful is most likely making a grievous error. . . ."
To read the entire July 2003 column, follow the link to the right.