RoyalTiger, this sounds like so many other stories on here. Cheating and betrayal is a very tough thing to process. You seemed to have handled yourself really well the last time you saw your ex. You were able to stand your ground whilst not creating or reacting to any drama--this is really, really good.
I'd like to know what questions do you have, just off the top of your head? There's no wrong question. Are there some things about BPD that you want more clarification on? I would imagine you are also having lots of thoughts/emotions post-breakup. How are you feeling in this regard?
Looking forward to hearing more... .
To expand upon goldylamont's post. Learn about BPD and read the member stories around here, there are plenty to read about. Learn the patterns and cycles. I don't know if my ex actually has BPD but I know there is something mentally or emotionally wrong with her. From reading about BPD traits and reviewing my FOO, hell I may BPD. But I also know that this is a common thing with nons so I try to give myself the benefit of the doubt. She cheated on you. You don't need someone like that in your life whether she's BPD or not. Mine cheated on me too and I don't need that $hit in my life. How can you ever trust her again? It's over and will never work out. You'll never trust her or look at her the same way again.
In the words of my uxBPD, "I hate cheaters, once a cheater always a cheater"(projection?). My reply now after the fact is, "yes you are!" There's my dose of reality to live with. Stay NC... .