Would he be willing to send this other woman a "no-contact" letter, requesting that she no longer contact him, and that he was wrong to have let it go on as long as it did, and that he needs to work at his marriage?
Please don't underestimate the strong PULL of these things. Without a no-contact/transparency plan in place, unless one of the partners flat out DUMPS the other, the recidivism rate is EXTREMELY high in these things.
