Hope7, welcome to the board!

We're glad you're here.
I could have written all of this, Hope7. We've been together 7 years too, married for 6. At the beginning, my MIL used to tell me, "You're the only DIL I've ever liked." Overt warmth for the first year or so, characterized by zero boundaries. She talked to her son about sex, walked in on me peeing to talk to me in the doorway, shared really personal and inappropriate info about H with my mom the first time they met (info that could have destroyed H's relationship with my mom). Cooling by the second year, tension in the third characterized by some pretty tough, manipulative digs at me. Something always felt "off." H said his mom was quirky so I tried to be patient, not reactive.
I guess I didn't play the role she thought I should, so she began to split and now I'm fully painted black. Before understanding BPD, I couldn't understand why she was all or nothing. Nothing I did for her made her happy.
How do you remain empathetic? Frequently, her expressed feelings seem illogical and unfair. It is difficult to differentiate the truth from an imaginary scenario. When questioned later, she will deny saying certain things and change her story. It feels deceptive. She often misinterprets scenarios, which leads to anger/outbursts.
I so get it.
Learning about BPD really helped me understand the terror she lives in every day. It is a scary, scary world for her.
It also helped me clarify the
usefulness of healthy boundaries. I cannot remain genuinely empathetic
and sacrifice all of my needs - that creates resentment. What are your limits? What do you value, and how will you protect that?
Radical acceptance has helped me really accept that yes, her feelings are illogical and unfair but they are real to her. I am working on letting her feel whatever she's feeling without becoming defensive.
Low contact has helped me a lot too.

I need the space to stay centered for now, and that is ok.
I feel like she needs to be accountable for her behavior, but is that unfair of me to think?
It's not unfair, it just is. I feel that way too. It's a normal reaction.
The people around my MIL (H and her friends and family) will probably not hold her accountable. They've been conditioned to work around her behavior. I can only control my own relating to her. I spend time figuring out how to change my responses to her, like:
I've shifted the way I visit to ensure that there's an arrival and departure time and activities in between. This leaves minimal space for open convo.
I am prepared to respond in a number of healthy ways the next time MIL brings up H's ex and how much she loves her (ironically someone she hated when they were married).
H and I are in marriage counseling trying to get on the same page with some of this.
Do you feel there is any point in revisiting something that the person said during a heated moment that you feel was unfair.
If the moment has passed, usually no. MIL's beliefs about any conversation almost immediately shift to cover her own shame and meet her emotional/psychological needs. I've had some success responding in the moment (which incidentally is hard for me too because I don't think well on my feet). She once accused me of "never wanting her to live with us."
In the moment, I was able to use SET (support, empathy, and TRUTH).
I'd been through difficult crises before and a great deal of therapy. When I met and married H I felt grounded and healthy. About 6 years in with my MIL I felt crazy, and that's what brought me here. I totally understand the impact this can have. We all do.
Examples help us sort things out, so I'd love to hear a few if you want to share.
Most importantly, know that you're not alone!

pj