Hi Sunray and welcome to the family!

So much of what you've written is familiar. We "get it" around here.
It's so painful to be "pummeled" by someone we love and so bewildering, too. The splitting, the black-and-white thinking, it's hard to keep your head on straight sometimes, isn't it?
The balance you're seeking — honoring your feelings while also trying to cope — is a tricky one and one that I and others in relationships with pwBPD struggle with daily. It's an ongoing learning process, really.
You're taking a great step in getting therapy and looking at your own issues and behavior. That's great!

One thing I've learned is that my own behaviors and communication techniques were playing a part in the dysfunctional dance my uBPDh and I were in. By building up my own inner strength and confidence, learning how to keep myself calm and centered, I'm now better able to face his dysregulations. And, in doing so, I've found that those episodes tend to be lesser in intensity and duration (not always, but overall).
The Eggshells book is a great one. It's the one that brought me here. There are other books and resources members have found helpful. We've got a page of endorsed books and reviews here:
https://www.bpdfamily.com/content/book-reviewsSome tips I would offer:
1) Practice self-care. Indulge in hobbies. Spend time with friends or family. Take a walk. Do things you love. Anything that "fills your cup." That's a really key part to keeping your own physical, mental and emotional strength up.
2) Read up on BPD. You're already doing that, obviously. But the more you understand the disorder, the better you'll be able to face it.
3) Study and practice communication techniques. For instance, I know when I first came here, I was doing a lot of
JADEing (Justify Argue Defend Explain) with my H, not realizing that that tends to just throw gas on the fire. Much better to use
SET (Support Empathy Truth).
4) Post here. We're here to help and we have a lot of experience to share. Things can get overwhelming and we can help you break things down into bite-sized pieces. Also, you never know when you may be able to help someone else!
Here's another way to get started: Pick a recent incident (perhaps the one where you were communicating financial stresses to her) and describe it -- give a he-said/she-said play-by-play. That really helps us get a look at the dynamic and then we can give you some pointers or direct you to some workshops and articles that may be of most help to you.
I've thrown a lot at you there so take your time, but I hope you'll come back and tell us what you think and let us know a bit more. Again, welcome! And keep posting!