I'm sorry that that had to happen to you, Gary. I am a BPD diagnosed individual, so I can't really see it from your perspective, even though I wish I could. I can't answer why either... I don't even know if there's a "why" in this situation...
Perhaps you'd like to visit
http://www.borderlinefamily.com. It is the forum for "nons"- those that are involved with those diagnosed with BPD. All I can really say at this point is that I have made my past relationships feel like they weren't good enough even though they tried--- and it's kind of hard to explain , but I never wanted to do that to them, yet I still did. I just yearned and yearned for more love. It's so hard to say why because even I don't understand it. I just know what you are talking about, and I do believe it is typical for BPD sufferers.
I don't know if this helps at all, but coming from me, if I could have not had those problems, I would be a lot happier. I wish I could have just felt like everything was good enough and just saw things in a less confused light back then. But I couldn't.