welcome Blue41,
I'm glad you took the brave first step to post. That is the beginning of looking out for yourself.

It finally got bad enough that I left, I no longer felt safe.
I'm sorry to hear that Blue. Sadly its fairly common for our relationships to have outbreaks of violence. Mine did. Can I ask if you are safe now?
She finally told me she has BPD and that a month after we met she was so happy she no longer felt like she needed her meds, so she stopped taking them, cold turkey.
My Ex is diagnosed Bipolar 1 comorbid with another disorder most likely BPD. She was on medication and very compliant. Sticking to a medication schedule is very difficult and many people struggle with that. Was the doctor who prescribed for your fiancé aware she abruptly stopped her medication?
My experience was that medication helped my Ex manage her symptoms but did not cure them. It was more like medication helps manage diabetes. It was not like antibiotics cures bronchitis. If that makes sense.
I love her, so very much but when I left it was kind of dramatic and now my family knows everything. They want me to stay away from her and let her get better first. I want to give her a chance and stay, support her recovery.
I understand. I would encourage you to visit the very first thread on this board. The one called
LESSONS. There is a lot of important information there to help. Much of it involves looking at yourself first. which sounds counter intuitive but what has been observed over and over again is that changing our behavior/actions can make a huge difference.
Here is a link to get you started digging around in this website.
https://bpdfamily.com/content/what-does-it-take-be-relationship'ducks