I'm really sorry to hear this. Trust me when I tell you that it gives me absolutely NO satisfaction to be right about these things, but I did see the warning signs and I try to prepare people for it so that they're not so emotionally blown away when they find out.
How did you leave it with her after your confrontation?
Do you have any kids? (I'm sorry, I don't remember).
Is the OM married? Have you considered exposure?
I need to go back and re-read your sitch before I give you more specific advice, as the next 24 hours is very important, as is the next week. DON'T DO ANYTHING in the meantime! If she tries to talk to you, say one or more of the following:
"I have some decisions to make before we discuss this."
"I don't want to discuss this right now; I have some thinking to do."
"There's nothing to discuss about our marriage so long as there is a third person in it. End your affair, and we'll talk."
You don't need to be phony-chipper, but don't be glum either. Just reflect "resolve." Business-like; calm. I'm REALLY glad you got on the ADs when you did; that will really help you in the days ahead with what we need to do.
Final question for now, and I'm sorry to have to ask it, but have you had unprotected sex with your wife in the last few months? If so, you'll want to get yourself tested.
again, I'm sorry. But this does NOT have to mean the end of your marriage, unless YOU want it to. We're going to start driving now, instead of being an unwilling passenger on a ride with a woman at the wheel who does NOT have your marriage's best interests at heart.