Do the actions and behavior of your W fit within your values and principles? I gather by what you've said.......and mostly by what you haven't said........that her A is not a deal breaker for you. Is that b/c she said she had not had sex with OM? Or would that matter?
It always concerns me to see a man whose only worry is that his wayward W will eventually forsake her A and have him back.
One thing EVERY wayward wife has in common, and that is disrespect for her H. That is where you have to begin, if you want to have a good M, is her respecting you. I have a feeling it has gone on so long that you haven't really considered her not respecting you. A woman has to respect you as a man, before she can feel in love with you and respect you as her H. That's how women are wired.
So, evaluate the relationship and decide if she has lost respect for you as a man. Let me give you a clue. Any W who talks to her H about her time spent with her lover........has no respect for that H. The respect was gone before the OM ever came into the picture.
You need to also decide if you think it is wise to continue having sex with a woman who is probably having sex with another man. Please do not trust her word. Don't take chances. Protect yourself.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!