Lots of good points. I stayed because I knew the A was not about me. I had a strong enough sense of self that I knew I was going to be okay, even if the pain was very real. My fWW would sometimes say, "I know I broke you." I would reply "I am not broken, you broke our marriage, now we have to fix it, or let it end." I also stayed because she begged me.
In the end, and this may sound narcissistic, I knew she needed me more than I needed her. She was not good at the work, but she did it. She did the IC, found her issues and addressed them. In the end, I did the math too, did I want to go out in the world and find another partner, or did I want to stay, keep my family, and fulfill my promises.
Because the work was done, we have a very good marriage. Nothing will change what she did. But as we move on, because we have addressed the issues and both of us are healthy now. It is kind of like looking in a rear view mirror, the A is still there, but as we move farther away, the A gets smaller. Does it come up every once in a while? Yes. Then it gets addressed and we move on. No rugsweeping here, we have addressed it all.
BTW, the other thing that helped me was not dwelling on the APs. I recognized they were bit players in her drama, and they could have been anyone who showed her interest. They were small men with small lives, they were not worth my thoughts or sanity. That realization did not happen at first, but when I was able to let that anger go, I was much healthier.