BPDs are not to be trifled with. I went NC with mine several times, and she always came back...for her own gratification. It was never genuine, never real. Feigned affection on her part simply to reel me back in. The last time she came back to me, months ago, I was so far detached that I had honestly pretty much forgotten about her. I was never going back to the way I had been, and actually turned her into a FB of sorts. Since, I have met other people and just genuinely lost interest in her.
I am a firm believer that NC can only work--between two sane people that is--if the dumpER comes back to the dumpEE. If you go NC, then go and try and win her back, you're no stronger than you were when she dumped you. You also haven't found another girl yet, which as I stated before, is really the only way to get over your last broad. NC should never be about the other person, it should always be about you. In this case, I'm not so sure you really failed. If you're over her, at least. She opened up the door, you took a step in. If you don't like what you see, you can easily get out.
That being said, she is BPD so it's imperative that you tread with caution. I would of course advise you not to get back into it, and I think that's the path you're heading down, but if you do put two feet through the door just be wary that she is BPD and has you there for her own gratification...most likely.