Promise --
Sometimes you have to do things "just for you" and getting your feelings out to W, even if she doesn't want to hear them--"she gets angry and upset with me"--is very important for both of you. Part of her anger is guilt, pure and simple, and part is her inability to handle these discussions in a productive way.
Yes, it may seem "so easy to just quit right now and throw in the towel," but that's exactly what you CAN'T do. This is probably the most difficult thing you've ever had to deal with, with the very foundation and stability of your life ripped up and hung out to dry. Your marriage needs you, your W needs you--although she may not believe that. How you handle this devastating crisis will go a long way in determining whether or not either of you will gain anything from it. Don't waste your pain.
"I know why she had the A and what my downfalls and shortcomings were that led to it" -- it's vital that both partners understand that while the A was the poor choice of one, there was something in the climate of your relationship that led your W to think that this direction for her was the "right" way to go. You didn't cause the A but it's healthy for both to analyze what went wrong. You're right: discontent is no excuse, ever.
Where do you go from here? You've been in Plan A for a month, you're in the early stages of MC with W, she still won't talk about the A, you're still not sure whether or not it's on-going. Still many major issues to process. I think you need to find out what's going on. If she's still in the A, you're just spinning wheels for now.
So you've got to push some buttons for you. She needs to know that there are consequences to her actions and choices. Lay it all out, what you want and need from her and from your marriage, what the results of continued contact with OM will be. Be clear in your mind what you want out of this, tell her, and be certain that she hears you.
Keep us in the loop, Promise; we're here for you...
Ammon