Yup, sounds like your wife is having an affair to me. Why is she extremely defensive about it?! Because she doesn't want you asking her that question, so she wants to make it painful for you when you do.
My wife said she had "resentment" she couldn't get over too. Well, guess what? There was no resentment- it was a smokescreen to tell the therapist and best friend for why she wanted to leave me. In reality, she was hiding her ongoing EA.
Your M will not recover as long as there is ANY contact with the OM. Is the OM married? If so, I'm guessing his wife is in the dark? Popping the affair "fantasy" bubble and dragging it into the light of day would be my first priority.
