Well it depends has she assured you it will never happen again?
Is she working to regain your trust?
Did she tell you why and how it happened?
IF she didn't make sincere efforts to patch things up and you STILL want to stay married you have these options:
1.) Go out and find a woman and get even. And make sure she knows. Then she has an idea of what if felt like
2.) Make her pay by organizing a 3some with you her and another girl. And even if she hates it she should act like she like is because her marriage depends upon it.
3.) Make it look like you are having an affair to give her a taste of her own medicine but the problem with that if she doesn't really care or she could decide to use it as an excuse.
Personally I'd suggest asking her to pack her things and leave then file for a separation. Until you can get over it. That way she's out of sight and if she really loves you she'll stay faithful. If you find her about town with another guy well then you was never yours to begin with and you should dump her.
I knew 3 couples in a similar situation. One just tried to be more sneaky about it and cover her track better. The other wasn't just sleeping with one she was sleeping wth 3. He just caught her with one. The last they tried to give it a try but because she didn't really try to atone and because he didn't believe her he stayed angry and basically she used that as an excuse to leave. She didn't really try and turned into well you didn't forgive me and it drove me away. Which is b.s. because if you make a mistake you know you have to work at it.
You also have to factor what you may or may not have done to contribute to the situation but that doesn't excuse her actions. She's your wife and she should have talked with you before letting it get to that. I'd suggest telling her you have been trying to get past it but you can't and she needs to move out and also find out what she really wants cuz what she did was really fucked up. If you let her off light she won't take it seriously. Then I'd suggest seeing a counselor while she's moved out. And see a counselor who IS married or been divorced (though that might call into question their skill. lol!)
Avoid counselors that only have the "theory" of marriage. Otherwise is like listening to someone with no kids tell you how to raise kids.
Good luck.