Nodding my head at all of this. I knew that if I didn't cut my abusive mother off at 20 when I had the chance during my parents' divorce, I never would. She would become too embroiled in my adult identity, and I took advantage of the crossroads. It changed the outcome of my life, I know that, but without the closure I continued to draw other friendships into my life that mimicked her dynamic. Maybe they didn't swing fists but they were all needy borderlines who kept our relationship unbalanced, as I allowed myself to become inferior to their needs. Though I have never met her and hope I never do, I think it took my xH's OW to finally say, "Enough!" of these people taking everything from me while I sit there. THAT is why I was NC with him for so long (think I just had an a-ha moment about that) - because that archetype can no longer take my attention.
She's got issues that have nothing to do with you, MBIB, you know that. When you view it from this clinical space, whether it is NC or not, it makes sense to check out and let it play out. She can't be responsible for what drives you crazy right now - she is not capable of even her own sanity. But *you* are in the driver's seat (literally sometimes, with your EMT work!), so go with that and *trust* it is going to work out without your hands on it. If you are afraid letting go means you don't care, trust me - it doesn't. I still care very, very much, but in a way that doesn't further complicate either of our lives. But I do agree with In It that these people are also after financial gain. I know that's it in my case (verified by what she told a friend of mine) and I am near bankruptcy.
As for the dynamic between the two of them from the xH's perspective, this OW also mimics xH's first girlfriend, who at 16 moved in with his family so he could "save her" from abuse. She cheated on him with a boy from another school during that time, and he was still forced to cart her around and be her savior because it made his parents look good at their church. It is not a shocker that his affair partner has so many problems and needed rescued from her own marriage, and that again, my in-laws and complicit. And right after BD while he was still here, we saw the old girlfriend one day at a store. He was texting OW at the time (Monster LOVED to do that in front of me), and it was as if he'd seen a ghost. I actually believe there was a time he combined the two mentally. He would play this song over and over that he'd written in high school for the old gf (long before me) around this time, too. So much unfinished business for what we all assumed were distant memories! Is it lack of serotonin drawing these memories out? Would this have happened without a chemical imbalance? I hope we have the answers someday.