If we ever come out the other side there will be an entire unknown story that may be revealed and need to be recovered from.
I know there is nothing to be done at this point and I try to not think about these things. It is just difficult.
Let me lay out a scenario for you. Let's assume your W decides the grass may be greener somewhere else. She met someone, maybe before you separated, maybe after. You separate, she pursues it. Of course, you don't have much contact with her during this time because she's completely involved with someone else. As with most affairs (if you even want to consider it an affair), it eventually dies a natural death. She realizes that maybe the grass isn't greener.
Somewhere along the line, she starts thinking that maybe you weren't so bad, maybe there was more good in the M than bad. Maybe your M problems are fixable. She reaches out to you....just to test the waters. Maybe she's thinking you could start fresh....start as friends...maybe build this into something new.
So maybe this plays out for a few months....and then she tells you about OM. How do you react? What if you had been seeing someone? How would you want her to react? Would it really even matter?
If it's a deal breaker for you, or if you have a problem seeing her if she's involved with someone else, maybe you should just ask her the next time you see her, "so are you seeing anyone?" And if you do, be prepared for the answer.