That woman is SO LUCKY. You have given her the most beautiful love. Acceptance and forgiveness would seem impossible for many men, but you are right there with it. BLESS you.
Your W really needs some help, no matter what happens with your M. She craves something that she doesn't get at home. Whether it's healthy or unhealthy, the root of that craving has to be identified (I think through counseling) so that you can understand and meet her needs. If that work doesn't happen, she'll just stray again.
Perhaps couples counseling and individual counseling (for her) can start now, regardless of her moving home? You've GOT to communicate with her about the root of the problem. She needs help "getting it". Even if she read some of the posts on these boards, she'll get it much quicker than just floating out there acting on whims and being influenced by the actions/pursuits of other men.
As a matter of fact, I would demand it as part of your terms. Counseling, right now, to get down to the bottom of this so you can be her "one and only" forever. What do you think? I'd bet she'd be open to it. At the very least, it would provide a forum for her to flog herself and ease some guilt.