Hi Isla Green, we're glad you landed here on the boards
you'll find yourself in good company with others coping with the pain of having a family member with BPD.
Your description of how your mom's behavior escalated after you moved in with your dad actually made a lot of sense to me.
pwBPD (persons with BPD, whether officially diagnosed or "just" traits and behaviors), struggle with balanced thinking and emotions about relationships, especially close relationships.
One term for that kind of extreme thinking is
"splitting", where the pwBPD can't hold a perception that someone has both good and bad qualities at the same time.
I wonder if your mom struggles with that, and can't accept that you can love both her and your dad -- instead feeling "you have to pick me or him, and if you pick him, it means you're bad and don't love me".
Do you think that could be part of it?
...
While it can be challenging to have a safe relationship with a parent with BPD, it is possible when we value ourselves and our needs, and work on learning more about
true boundaries and values.
Settle in, check out some of those links, and let us know your thoughts on them, whenever works best for you.
kells76