A lotta people wanna cut Borderlines slack, give em the benefit of the doubt, feel sorry for em and stay on the relationship merry-go-round with a deeply fractured individual, largely because highly inaccurate web materials on the subject of BPD classify it as "a mental illness."
Borderline Personality Disorder IS NOT A MENTAL ILLNESS any more than Narcissism is! These two issues are diagnosed as "personality disorders," because that's exactly what they ARE~ and lest you forget, when your ex was first trying to seduce you, he or she was ABLE to appear totally rational, lucid and sane~ or you wouldn't be gasping in pain right now! (One with a REAL mental illness can't fool ya like this.)
Yes, we can feel sorry for those whose earliest life experiences yielded significant emotional deficits, but they're NOT mentally ill, and you've gotta QUIT thinking of em as such! Besides, if you've been drawn into one of these relationship experiences, YOU suffer from the same deficits as an infant and thru childhood, that a Borderline did~ ya just got better at coping with em (which typically turned you into someone with a Savior Complex).
You should NEVER have to walk on eggshells (the title of a lousy book on BPD, in my opinion) in a love relationship! You should never have to censor your true thoughts or feelings, you should never have to bend over backwards to please someone, you should never be guilted or shamed by one who (supposedly) loves you, and you should NOT TOLERATE ABUSE from anyone~ regardless of WHO the fuck they are!
Understand fully, that if you've accommodated harsh treatment in your romantic OR platonic involvements, it's ONLY because you've been programmed to normalize and accept it, since infancy!
Here's the deal: You can't repair or fix anyone else. The ONLY person you're equipped to repair, is YOU~ with the help of a highly competent professional.
Another thing you MUST allow yourself to accept, is all the sympathy and compassion you wanna give your BPD lover or ex, directly relates to the aspects of fragility and vulnerability you've discarded in YOURSELF since you were very little, in order to play "the Hero" in all your relationship dynamics!
This is called "projection," so all your efforts to save and change someone else, reflect how much you actually need to save and change YOU.