Pulling back will not feel natural to you, so expect that....ok? What you "feel" like doing is to pursue her. That's the way men are wired. When you are afraid of losing her, then your natural instincts scream out to grab hold of her. However, it doesn't work when she's a WAW who has lost her attraction for her H and has her attention on the OM.
She's different now. She's not an inexperienced teenager any longer. She's looking for something in this OM that she didn't get in her R with you. I know you want to trust her. That's only natural, too. I suggest you don't ask her questions about OM, her behavior, intentions, past actions, or anything other than what directly concerns the kids. Tough stuff!
Healing from an affair, even an emotional A, is very difficult b/c for the woman, her heart is involved. For men, they have a harder time dealing with a physical A. Either way, it is a rough road and it takes a long time to work through it. She's had a taste of the infidelity drug now, and let me tell you....it is a very addictive feeling.
I'm telling you this so you have an idea of what to expect. Don't throw in the towel, but learn by reading information on line about infidelity and how if affects the wayward spouse and the LBS.
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!