What can I do to save my M?
In order to save your M, you need to be willing to let it go.
How did the 180 end? Did it just fizzle out? Did he come around and then pull back?
At this point, you only have 2 options:
1) Confront him and tell him to get out. Make a copy of the VAR recording and then play the copy for him. Do NOT let him have the original. Let him know that, as gut wrenching as it was, you heard him, and you know, and you're done. Give him NO options.
2) Don't confront and let it go on forever. Yes, you'll be unhappy and you'll know he's cheating as he's been doing for years, but you will have your M.
Right now, you've confronted 2 times, and both times he's had no real consequences. He risks nothing by continuing to cheat. By being willing to lose your M, you are telling him that you will NOT tolerate this for one more minute, and if he doesn't choose you and his family, then he will be 100% out. Anything less lets him continue to have it all - wife, children, girlfriend.
If he leaves, then yes, the M is over, but isn't it already over if that is what he would choose? Do you want a H that is there out of obligation and is actually in love with another woman? Of course not. So, he needs to see that he cannot have both. You must be willing to lose the M to force him to decide, once and for all, what matters to him.
If you aren't willing to do this - if you're going to just let him ride out his A, no matter how long it lasts, then why bother confronting? If you're going to let him have a girlfriend, why add to the tension by telling him you know?
I'm so sorry you had to hear him speaking to her like that. How sickening. Do you really want him after all of this? If so, why? Do you want him, or is the thought of him not being there overwhelming and too much to deal with? If the latter is the answer, that's ok. Really, it is. This is hard, and adding the thought of an entire life change makes it harder. There is no shame in the fear that comes with this.
However, if that is it, please, for your sake, find an IC that can help you work through some of this. You deserve so much more than this. He is treating you terribly, and the lies he's told to have already gone through 2 DDays, and now this? No - you deserve more. Much, much more.
((((hugs))))