Ya, I relate. Your story mirrors mine - HEY wait a minute . . .
Seriously, I relate and was stuck at wondering if I was at fault. And it is a valid place to get stuck at, not because it is your fault, rather, because you, like me, probably did things that you feel bad about and so thought maybe she has a point.
Whatever was my "fault", weren't the underlying motivations that drove her behaviors. I could (and had moments of) being very nice and easy going about it all; yet, it did not make a difference. Because, I was not the central issue with her to begin with; BPD was/is.
Remember, PD is an emotional condition that is triggered with emotional intimacy. The fact that you were close to her an she felt close to you is the "fault"-line that triggered the emotional outbursts.
So, part of having a balanced perspective is coming to understand that you are not the cause of her problems. Second, you cannot control her problems via accepting blame and most importantly you cannot cure her problems - as in, she is not suddenly going to see the good side of you and have an aha-moment and change her mind. The opinions she has of you and her behaviors towards you are at most indirectly about you. Indirectly in the sense that you are the object of her emotions and therefore the target of her internal bad feelings. While she may intimately "know" you, she cannot become emotionally attached to you without the total encumbrance of fear of abandonment; the central reason why you are at fault, a ba person and never do anything right!
While we leave these relationships wondering what happened; over time, we come to see that the relationship itself was with someone who appears present in many areas of their life but is not aware of significant emotional liabilities. Explicitly, if your ex has untreated BPD, she is emotionally unavailable - that is the diagnosis of BPD.
It is a hard pill to swallow and one that slowly goes down while you choke on it. I don't mean to sound terribly dour but do wish to make an impression on you that this is not your doing. Take responsibility for what you know you could have done better or need to work on. For the remaining pieces there is BPD family; the posts, the articles, your fellow non's.
JRB