Hi Shell-Shocked, welcome to the community.
I agree with you that having a relationship with a partner with BPD can be difficult. I personally have experienced the roller coaster ride of high points and low points myself during my relationship with an ex-gf who had BPD. It can be tough and exhausting.
When we are dedicated to improving a relationship, one thing we should try to do is not make things worse. Human relationships are difficult even when both parties are relatively healthy. A person with BPD can be even more sensitive than the average person so its tough for them and tough for those of us who love them.
Have you read this article about how to handle conflict:
https://bpdfamily.com/content/ending-conflictMaybe check it out and see if it makes sense to you. And feel free to keep posting both questions about the article and questions about your relationship. Many people here understand what you're going through because many of us have had the same types of experiences you've had. Hang in there and a virtual hug to you.