Welcome to the site, glad you found it - sorry it was necessary.

Absolutely there is a huge toll on caretakers of pwBPD - it comes in different styles, but it really is one of the most absurd mental health quandries to caretake because it's unique in that it craves sympathy and attention - but then needs to attack whoever is trying to help them or offer sympathy or attention.
Because there's a not-entirely-unfounded connection between BPD and adverse childhood sexual incidents preventing a natural parental bond, parents of our loved ones often have an entirely different struggle - seen as having caused it by either participating or not protecting. As long-term loved ones who are not the parents, we have a slightly different battle - it's not the same as those who are just upset because their boyfriend/girlfriend of six months is crazy, it's decades of caretaking the crazy...and getting slapped, slandered and occasionally stabbed for it.
For what it's worth, it was absolutely amazing to me the absolute change in my anxiety levels being able to participate in the in-person Family Connections support group/class for caretakers. Finally I had found ACTUAL peers who ACTUALLY understood. I'd strongly recommend it, because meeting with caretakers of non-verbal autism or caretakers of alcoholics or caretakers of bipolars is just not the same.