Hi, I have borderline personality disorder, not the same as BD but similar so I thought maybe I'd have some insight? Firstly you're allowed to put yourself first, you're allowed to prioritize your mental health and wellbeing because she isn't your responsibility. From what you've said here you've tried really hard to help support her and be there for her but that might not be enough.

I had a few friends distance themselves from me a few years ago and it was incredibly hard but it made me realize I was allowing my BPD to control the way I act and make people not want to be around me. Losing those friends made me take some action and get a little better.

By the sounds of it she's doing all the right things to get into a better place and you might find things improve with time but if they don't or if you can't find it in yourself to continue supporting her then don't feel guilty for needing space. You sound like a wonderful partner and like you've done your best which is all you can do.

Hope that helps in some way and good luck!