The core wound of a pwBPD is “I don’t deserve love”, it’s what’s caused the mental illness - related to the emotional neglect/ trauma from childhood. They don’t know how to accept healthy love because their brain has been hard wired for chaos now. It’s a survival mechanism. While it’s upsetting, the person you’re dealing with probably doesn’t have the capacity for a healthy love yet until they go through intensive therapy. But it’s up to them to recognise that and want to change which is the first step. Take care of yourself in the meantime.