I'm so sorry you are going through this. You've been getting a lot of great advice so far, so I won't add much in that regard. But I thought I'd comment on the marriage vows part as that was something I struggled with as well. My quick story is my XH had EA that turned to PA, MLC, and left me and is living with OW now. Raised his two kids as my own. Divorce recently finalized.
When it came to my values and my vows, I did try to do what I could to save the marriage because I held my commitment to that in high regard. However, with the situation as it was, I made an effort to ask for the opportunity to reconcile (without R talk pressure) a few times, asked for him to end his AF, and I refused to be the one to file for the divorce or help him with the process. So there I stood up for my values. For me, the only choices I had were to move on from the MR or to remain in a relationship with him and his AP. Part of that was I could never be in a MR of three, but part of that is that he was stealing money and I needed to protect my share of our assets. My ethics told me that accepting the D was the best way to live out my core values. I can sleep at night knowing that I tried, in the ways I could, but it takes two to make that process work. My XH refused. And hell, we did a Gottman retreat only a few months before he started his AF....so I agree, MC doesn't work in most cases.
The thing with the MLC part is also that the whole process takes a long time (if it ever resolves). And honestly, I am no longer feeling that I would want my XH back after all the deceit and his covert narcissistic behavior. Maybe it is mostly his MLC personality, but unfortunately, as time goes on, I struggle to know if the person I married was the person I knew. My IC and I both feel that my XH will turn around at some point and try to come back (hell, I did everything for him, so I would miss me too! hahah). But if I wanted to try again, it would be a whole new R anyway, so knowing that I still accepted the D. The D is a way to protect yourself legally. If you wanted to stand for her, you can still stand...and be divorced.
Anyway, I hope that provides more food for thought. You do sound a lot stronger than I was at the beginning of my journey. You are doing a lot of things right already, so just keep moving forward day by day. The folks on this site are amazing! I am not sure what I would have done without this forum!
El
Me 52, H 56 T10 M7, 2nd MR for both 2 Step Sons (19 and 21) BD: Fall 2020 D finalized: July 2022 XH Married AP soon after D day.