Your conversation could be a script from my conversation with my W a month and a half ago. What is going to follow for the next few weeks/months is up to you now. But there is no denying one thing. This is going to hurt. Bad. You are going to have good days, but mostly bad, painful, miserable days where you need to hide away and cry.
Judging from what you say above, you've told your W that she needs to stop seeing OM. You've told her you will leave if she doesnt. But then you asked her if she wants to work on the marriage and you continue to make plans with her and her mom. That's telling her you're not going to leave. She has no incentive right now to end her A. Most likely she hasnt.
Now you need to actually follow through on your words. You need to GAL. Without her. She's fired you. Go to the gym, call some friends. Be too busy for her right now. Let her know through your ACTIONS that life will continue with her or without her. Stop talking to her other than to answer simple questions. Do not talk about the A or your M or ask her if she's ended her A. Don't ask her if she wants to work on your marriage. She doesn't right now. Why would she? You're still hanging around asking her if she wants to save it even though she's with some other guy.
I'm right there with you in the same scenario right now. But things are a little better because I moved from the stage you're in to talking to an attorney, making preparations to leave, and figuring out visitation/custody schedules. This all scared the crap out of me, and I didn't want to do any of it. But it scared my W more. And as far as I know, she's leaning toward working on our M. I haven't asked her, so I don't know.
What I do know is I had to stop having conversations like the one you had above and start working on ME, and showing her that it's better where I am than where she is.
