I hope you are still around. Whenever I don't see a newcomer posting almost daily, I get concerned. You really need daily support for quite some time.
I want to stress the importance of seeking a plan that will help your W overcome the strong urges she will have to continue the A. Quite frankly, I don't know if she can do it while she continues to work in the same office with OM.
If you have not read about the addicting power of affairs, then google PEAs and see how it affects the brain. It's strong stuff and causes well intentions to crumble. If she ends it, then she will actually go through a withdrawal period. That is why she will need a plan to get her through it....or she will succumb to his advances or her desire for those "in love" feelings to continue.
This is not an easy thing to hear, but you need to know what you are facing. It will be incredibly difficult for her to go the first 24 hrs without contacting OM. So, she needs to have something and somebody who will give her support during those times. The hours away from the office need to be filled. You cannot stay glued to her hip or expect her never to have alone time. That's why the two of you need to agree on how you will protect your M from further contacts with OM. I suggest an outside source b/c otherwise you and W will be too easily upset at each other. Everything will be a trigger for both of you. If you have an experienced person (not related to either of you) and preferably a professional/pastor/priest or program to lay out the plan, then she won't take it as defensively as she will from just you. It's like working with dynamite. Won't take much to make it explode.
That is why it's important that she is truly remorseful and wants to really "work" on the M. Sometime, a woman will choose to do the right thing.....and then those other feelings will follow. So, if she is doing it b/c it is what's right....accept it and be glad. Her feelings have to have time to change, or to find what those true feelings really are again. She may not feel true remorse for quite a while. That's hard for you to understand, but for a woman it involves so much of her emotions. She may experience small does of remorse as time goes by. It depends on how resentful she feels about the past and your part of the M breakdown.
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!