Note - this all seems so cut and dried right now, but I wonder if it's easier because she's out of town and I'm dealing with this without her around. When she's home next week, how will I react? If she was in the next room while I typed this I would be able to "take my temperature" in a real way. What if I lose my nerve to be so matter-of-fact? Face to face is so much different than having a discussion with myself and inserting what I think she'll reply with. Then again, when she's been here lately it feels like she's out of town anyway...
Just a random thought. Need to steel up.
You need to be aware that your wife will very probably try to gaslight you when you confront her. She will tell you that the affair was your fault, because you mistreated her. She may invent wild stories of abuse to tell your friends and family in order to discredit you, or she may try to explain away things differently than they actually happened.
For example, if you had an argument a month ago, she may describe it as a monumental shift in your relationship that practically forced her into her affair.
Either way, don't fall for it. Some betrayed spouses start to question their own memories of events and wonder if their marriage really was closer to the hellish nightmare the disloyal spouse describes. The more likely scenario is that your wife wasn't blissfully happy because you had a marriage with real problems, the way real-world marriages usually do, so she started banging other men to cure her boredom.
Assuming you want to divorce, I think the most pain you can inflict upon your wife is to stay calm and tell her that you don't intend on fighting for her because she isn't worth fighting for. Appear excited to get back on the dating scene and start doing your own thing. Her affair fantasy may involve you tearfully begging her to stay or you angrily fighting off the competing man.
And as soon as your timetable for exposure comes around, you have to tell the other man's wife. That could put a serious crimp in your wife's lifestyle right there. If he has to break up with your wife because he wants to save his marriage, well then your wife winds up with squat.