...
I'll also repeat my caveat that each pwBPD is different, and some pwBPD are so impaired, or have other issues as well (addiction, etc), that this discussion isn't a promise of "oh, if you'd just authentically validated more, you could've saved things". Some relationships aren't livable. ...
I'll add that in the example I gave, this was really hard for me to do because BPDxw was so obviously cruel and spiteful to my mom, and also me, whenever in her mind I demonstrated any sort of concern for my mom whatsoever.
It was almost scary; like this wasn't just like a sitcom plot where "
she doesn't like my mom"... it was more like "
she actually wishes my mom was dead, doesn't want her to ever see our daughter, doesn't want me to have a relationship with my own mom, and will do and say anything to ruin this whole thing."
Looking back, I see her issue was jealousy and her own paranoid & unhinged fears that anyone else in my life - even my own mother - was a threat to our relationship. I went along with some of her demands, and saw & spoke to my mom less, and she saw our daughter less, during these years, and in hindsight, I wish I hadn't, because it wasn't ultimately about my mom. I know if I cut my mom out of my life completely, as BPDxw was demanding, she would just move on to another demand, because the issue was entirely in BPDxw's head.
As you said above, some relationships just aren't liveable, and that was how this went. In order to keep BPDxw "happy," i.e. not in shrieking fight mode, or making-a-scene-in-public mode, or not actively-insulting-and-attacking-my-family-members mode, I would have to give up too much of my own life and relationships with my family. What was I getting in return? An unhappy, insecure, ignorant, and abusive wife, and a lifetime of knuckling under to her demands, even at the cost of my own and our own daughter's future? No thanks.
It is, though, important to remember that if you're interested in healthier relationships in the future (and I think many members here on Detaching are), remaining fully in the "there was nothing I could've done, she was so irrational" stance hamstrings you from learning the relational tools and skills that will benefit you in your future intimate relationships.
Hardcore working through
how to stop invalidating others could be a really good investment in your future relationships

It'll be interesting to hear more analysis from the group about healthier, more effective ways (besides JADE-ing) to stop the cycle of circular arguments.
I agree with this, and the experience has benefitted me in other situations, like at work, when I recognize people who thrive on conflict and how to handle them, particularly how to be assertive without getting upset or escalating things when someone is pushing your buttons. I had a hard time with that; I was either worried and afraid of opposing someone, or being pushed past my limit and exploding in anger.