Hello, maybe2morrow &

I'm sorry that you are having to deal with something that feels like a betrayal; whether your Ex (or current?) girlfriend is BPD or not, it's a very painful thing to have to deal with. It sounds like she's trying to make it work with you, but your suspicions and hesitance to trust her again (which is understandable) is getting in the way of that for you. I do know how that feels, and it's very difficult to get over.
Have you had the chance to read some of the information on this site regarding BPD? We have a couple of Articles that can give you some insights into BPD if you are curious if she would be diagnosed with that or not (or maybe have some BPD traits):
Article 2: The Symptoms and Diagnosis of Borderline Personality Disorder and
Article 3: Borderline Personality Disorder - A Clinical Perspective. Whether BPD applies to her or not, be sure to check out the
links to the right-hand side of this page to learn about difficult relationships, or difficult situations in relationships, in order to try to make things better.
There is always the chance that your girlfriend is having a hard time with a long-distance relationship, or she is torn between you and the other guy, or she is sincerely wanting to stay with you and is sincere about not continuing with the other fellow... .It's really up to you to decide if you can come to the place in your heart to trust her again, or if this other guy will become a sticking point for you too painful to get over. Keep posting your questions, and reading all you can on this site. Hopefully with more understanding of BPD you will figure out if she is suffering from that and specific communication tools would be good for you to work this out with her. Or if she's just a normal woman struggling with her feelings right now--or not struggling but having a hard time convincing you that she is trustworthy... .
Regardless of the truth that you turn up, we are here to help you, maybe2morrow