I like KissTheRain’s explanation. It fits in with what I’ve been told.
I have a friend who has borderline PD and some things are very obvious. She has the ‘I hate you, l love you’ thing. She is also frequently suicidal but it’s often manupulative. The police are involved etc and it’s really messy. I’m not saying others are like this but my friend is.
I used to wonder if she also has bipolar and if I also have borderline PD. But I’ve known her for decades and I would say my diagnosis is accurate as is hers.