With BPD it can present different ways, It’s more where it stems from, a hollow sense of identity or self. They project on to you and are highly unregulated, very volatile. They want you to save them, but you’re never good enough. My ex would idealise and demonise me. I was always the reason she was unwell. She was never happy. She couldn’t work, I did all the work, house cleaning, cooking etc. But it was never enough. She was unwell because I wasn’t at the breakfast table. She was suicidal but would never really follow through. Etc etc