His wife? That adds a spin to it. They're both cheating. They both think that something is lacking in their relationships. That's clear. Does that make it right? Hell no.
YOu have to decide whether or not she's worth the trouble, the difficulty, the pain. If she is, that's a starting point. Hell, showing her you want to make it "better," make things in general "better" (whatever the f**k that means) could do a lot. But, do you care enough to do that? If you don't love her, cut it lose, let her go, it is best for both of you. That is the first thing you need to figure out. If you do love her, is this pain and frustration (and work) worth your time? Are you willing to try and improve things, and do you think you're able to put these transgressions on her part aside? If yes, yes, yes, etc, then you have enven more to work with. There's a lot of questions you have to answer for yourself before you can really know where to go with this. Worry about that first, then what to do second.