Hi Rose77,
I come at BPD from a slightly different angle, my significant other (SO) has an undiagonosed BPD ex-wife (uBPDxw), but I did want to stop in and say welcome

I'm sorry to hear you are struggling any break-up is hard but seems it's doubly hard when your partner is BPD or has BPD Traits.
Can you tell us a little bit more about the relationship? How long have you been together? Are you living together?
I seek advice on how to break up and leave my abusive partner. Everytime I initiate a breakup he threatens to defame me or cries and I become weak and go back.
It sounds like he is using what we call FOG (Fear, Oblication, Guilt) or emotional blackmail to keep you coming back. Below is a link to more on FOG. I think learning to recognize the FOG is one of the most helpful things you can do for yourself. In my opinion once you recognize some BPD behaviors it can help to take things less personally which can help with detaching.
https://bpdfamily.com/message_board/index.php?topic=82926.0I also want to point out the box to the right ---> each item is a link to more information please feel free to check out anything that resonates.
Take Care
Panda39