Thanks, everyone!

What kind responses. I'm sorry for taking so long to respond--I was afraid to check back because I felt embarrassed for expressing anger on these boards, when I know everyone has to deal with so much anger from the pwBPD in their lives... .ANYWAY, yes,
Penny123, I think I do need to see a therapist! I've tried a few, who've helped in their way, but I'm not sure how to find the right therapist to discuss life with a pwBPD... .
I am more assertive than my husband, so I am better at dealing with his mother. He lets a lot of anger build up inside because he is too afraid to confront her when she acts badly.
Right now, MIL is threatening to go no contact with her sister, who has been generous, kind, and supportive to her ever since she was diagnosed... .So why the anger and abusive behaviour towards her? Apparently her sister should be able snap her fingers and save my MIL's house form foreclosure.
My husband is disgusted by this, of course. I try to be supportive and let him vent about it, but he cannot do the same for me. It's too much for him I guess? On the day I started this thread, I did vent a bit to my sister and mother, and I came to the place where I felt heard and could feel some compassion for my MIL.
I would LOVE for her to have assisted living,
Penny123, and I think it would be better for her, really. She enjoyed having a nurse and physiotherapist come in weekly to help her recover from a recent flu. (Some irony: she thought the physiotherapist talked far too much about herself! I had to laugh about that because MIL doesn't normally let anyone get a word in edgewise.) Because she is still capable of making all her own care decisions, I can't arrange it for her. I could try to convince my husband that it's time to move out, and she would have to arrange some other care, but I don't think he'll agree to that yet.
leenlou, I don't think I will ever love my MIL, unfortunately. She's funny, she's sassy, but she's not someone you can form a bond with because she's so self-absorbed. Sisters share a closer relationship, somehow, I think. I can't imagine going NC with my sister, even though she can be challenging (I honestly suspect her of having mild uBPD), so I really feel for you. It must be so difficult. I hope that self-care is making a difference in your emotional well being. I need to get better at that, for sure!
Woolspinner2000, I think you're probably right! At this point, I would say that my MIL is more self-absorbed and less empathetic than my uBPDh, but just a couple days ago he said something like "I'm so much like my mom, I'm so sorry for ever being a jerk to you." So yes, they are similarly emotionally dysfunctional... .If only my husband could like, take that self awareness and actually CHANGE his behaviour, that would be great. Baby steps.
Yesterday he had a particularly difficult time with his mom, and then had a meltdown towards me where he threatened to cut off contact with me until the weekend... .I was thinking: "wow you are literally acting like your mom just did, what is wrong with you?" But I'm doing my best to be accepting of his emotions and need for space, even though I kind of feel like making a post in the "Conflicted" board... .At least I'm away travelling right now, so I don't have to deal with the drama in person. That's probably made him feel even less stable, though, what with the fears of abandonment and all.
I need to get better on letting go of the drama and emotional pain! I get so anxious about him, to the detriment of my sleep and self-care... .Ugg I really do need to find a therapist.