OP, I feel for you, I just went through this myself and it has been extremely hard on me.
My husband cheated on me and things have never been the same since.
You said your wife was a virgin when you met, well, I'm thinking that because she hadn't had anyone else before, that maybe she was curious after all these years and her curiosity got the best of her.
My husband had only been with one other girl before me and I kind of think that maybe he was curious as well, although he was also very intoxicated, both things may have played a part.
At any rate, things have not been the same since, we have been to counseling, we've tried separating for a bit, but I still have that wall put up, and I don't see things getting any better.
On top of that, I now have a curiosity for other men. I have an extremely high sex drive and some fantasies that he cannot full fill due to him being a very plain jane type of guy.
The story goes on, I wont get into it, but I just wanted to chime in on this.
I wish you all the best. Only you have the answer.