I believe she really wants to work things out but she says she can't "turn off the switch" and stop loving the OM. Right now she's not sure she can ever get over him.
ALL, and I mean ALL, contact with OM HAS to stop NOW. It's your call, but for me, this would be non-negotiable. Goes along with what I have seen gucci and puppy post - "I will not share my W with anyone."
She has to agree to full transparency - she gives you access to her email accounts, cell phone records, whereabouts, everything. I'm sure I have left some things out, but you get the picture. If she wants your trust, she's gonna have to earn it back. This is the first step.
Are you sure that OM's W knows? I assume she was a "friend" of yours? If so, and assuming she knows, why didn't she tell you? All I'm saying is (and to borrow another phrase from puppy) "All cheaters lie." Just cuz your W said OM's W knows DOES NOT mean it is so. I would reach out to OM's W and make sure she knows. You would want the same from her.
