So for me, I don't let my husband play the victim.
I don't say that to be mean, confrontational, or unsympathetic. If he wants to spend 8 hours in the car, leave a day early, be crabby, whine about how she treats him poorly after doing her a favor, and miss out on a New Years kiss from his wife... .
That's his fault. Not hers.
Because I can't change her. And she's doing what she loves to do, which includes making everyone know that she's the boss. I won't enable him playing the martyr though, because that's not my job.
My husband has helped his ex-wife move 5 times. Every time she does not thank him, complains about his timing, and once yelled at him for dropping a washing machine ---- that we GAVE HER.
So after the 5th time, he came to me with the same old song and dance, and I simply said
"I don't help people who don't appreciate my efforts, maybe you do. At this point, you either accept that she won't and help her with no expectations -- or you don't help her because your expectations are not being met. Your choice. But this where you keep complaining isn't working for me." And he made a choice. He helped her anyways. The complaining went away. And the next round, he said "no"... .and she's never asked again.
As wives in these relationship dynamics, it's easy to align against the nonsense that is the ex. Commiserate about how she is acting like a person with BPD does. I get that. She's never going to change though. In my case, my husband did not change either. I simply grew tired of all the drama. The pit in my stomach. The nonstop crisis situations that don't make any sense. I accept that.
He still has crappy boundaries in his relationship with her.
Him and I have really great ones though in our marriage... .and mine with her as well... .one of them being that they get to deal with each other and not engulf me in the flames of their relationship.