I agree with what Leo said. From what you say, your wife seems unwilling to acknowledge and work through the problems she is dealing with, both personally and maritally. Perhaps she was looking to you because you are older to fill those gaps. Until she focuses inwardly on herself and does some work, she will repeat the same pattern. Running away to another relationship where she can start fresh will not work. She needs to run to a therapist's couch -- don't allow her to engage in friendly conversations with you about this. Set your boundaries and let her work through this on her own.

Easier said than done, for sure. Good luck to you.