Many WAW who are already seeing someone or have someone in mind, try to make it look like they are separating first THEN seeing someone. It is the only hope they have of that other man being accepted as a replacement for you. It legitimizes the relationship instead of it being an affair that wrecked the marriage. This may not be what is happening, but it usually is.
Depression and low self esteem or self confidence are a breeding ground for affairs. The person is unhappy and seeks out the comfort they need in someone elses arms.
Also, its not really dating as you put it. Its a self act commited by someone who is unhappy and puts their own needs ahead of their spouse and family. They through themselves recklessly into another relationship.
Anyway, if this turns out to be the case you will deal with it as it comes. Just wanted you to start thinking about it as a possibility so you are not stunned if you find out. And so you can avoid becoming angry or mad to the point where you make things worse...that is, IF you still would want her back. And you might very well be willing. Dont discount that position because you would be surprised the things you would be willing to look past. We all thought our wives would be out on the streets if they did such a thing, and here we are seeking help to win them back.
I understand what you are saying. I'm not sure if it matters, but she is going to therapy; she is still in contact with my mother; and she has not changed her status on FB. (If the day comes that changes, I really don't know how I will avoid falling apart.) She keeps asking friends, family, and my therapist if people can change. She keeps asking if anyone can guarantee those changes will last. (Of course, there are no guarantees in life.)
As for myself, I think I could forgive an EA, but I just don't think I have it within me to forgive a PA. I have been living in a SSM for the last few years and she constantly dismissed my attempts to talk about it. To run to someone else seems unusually cruel.