Thank you, this is what I was leaning towards. I do feel like a bad person and I worry about my parents reaction (they are still hoping I will let her back in my life after I have "had a break").
Guilt for myself and yearning for good mental health is always part of the package for me. As zachira said, having a bpd family member is a lifelong sorrow
I wonder if your parents have not yet grasped the extent of BPD. It's common for parents to want good outcomes for their children and deny the illness or the fine details of it. It may place an unfair burden on you as they may be pressuring you to help your BPD sister get better. They may see that your sister doesn't act out so much with them if you're in contact. They may not see that the whole burden has shifted to you. This is what Notwendy points out as families needing balance when at least one element is out of whack.
Just guessing (and could be entirely wrong). My in denial father and PD older brother have done that to me (daughter) with my dBPD mother.