Well, if my wife cheated in such a situation, I would probably take some time apart. I'd need to clear my head and think about what I really want. Maybe I would talk to some close friends or family members for advice. They might offer different perspectives that could help me make a decision on whether to try to save the marriage or move on.
It's a really tough situation. You could start by gathering more information if you're not sure about the full story. But in general, you have to think about your own self - respect. If you can't forgive her, it might be better to end the relationship. However, if you still love her and believe there's a chance for her to change, you could set some strict boundaries and see if she's willing to abide by them.