What I don’t understand is, how someone can say I’ve abandoned them,
The simplest way to put it is that it is her perspective, it makes sense to her, and there is a rationale to it. Understanding or making sense of her perspective, right now, is likely impossible, when you're confused and in pain. It is a latter stage of recovery. I would encourage you to endeavor to do it as much as your emotional state will allow, it will ultimately help, but taking good care of yourself right now is usually priority number one. Almost anything you conclude, you will revisit again and again with new perspective as you heal.
One of the first questions members that have been broken up with ask (myself included) is often "but if they fear abandonment, why do they leave?".
More about brain chemistry than anything I did..
Both clinical borderline personality disorder, and bpd traits (or "bpd light") are about a great deal more than brain chemistry, and there is more than brain chemistry going on here. If it were brain chemistry, she'd "snap out of it".
Borderline personality disorder is essentially a world view. It is a way of seeing and interacting with the world. It involves pathologically seeing yourself as a victim, as others taking advantage of you, as distrusting others, as believing others have or will abandon you, and believing those things so deeply, so strongly, that they color the way you navigate and cope in life.
We all have a fear of abandonment and engulfment. People with BPD traits have then to a pathological degree.
Think of the fear of flying. Most people have a little. I can do it, but id prefer to drive across the country at far greater time and expense. Someone with an extreme fear of flying won't do it. They'll organize their life in such a way that they'll always go out of their way to avoid it. They may have an intense fear if their loved ones fly. They certainly would avoid a career or job that required them to do that.
People with bpd traits see these fears, where they may or may not exist, and they test you, and they test their fears, and in the process, they confirm them. "See? I was right all along!". Those fears don't necessarily go away if you "pass" a test. They may even grow stronger.
It is an entire set of deeply held beliefs, a way of seeing the world, and navigating/coping it.
I'm not sure exactly what her rationale is in this particular case. More than likely, it is a bigger picture issue than just the recent happenings. Knowing her, you would be in a better position than anyone here ever will be (we can certainly help) to grasp her perspective, but that's probably impossible when your emotions are everywhere, you're picking up the pieces, and everything is one huge puzzle. Trust me though, when I say it can happen, as part of healing. Theres nothing I didn't make sense of in my own recovery, no lingering questions, but, I "made sense of it" over and over again, with new perspective.
Right now, everything in you may be telling you to act, and to act now. If she is retreating, it is probably best to give total space and not push; she will only retreat harder. I had the same fear myself. My friends and family talked me out of so many moves that I nearly made. Please try to trust, that regardless of this "see you dont care you abandoned me" stuff, whether you never speak to her again, or whether she returns to you tomorrow, will not hinge on trying to prove yourself to her at this time.
If she returns, recovering from that will require a whole different headspace where you examine what was broken about the relationship, whether it can realistically be fixed, and how it's going to be. If she doesnt, the same is true as part of Detaching, but with more of a focus on how to take the lessons into future relationships.
Again, that probably feels a bit clinical and like we're getting ahead of ourselves. Today, cry, scream, ask questions, talk it out; whatever you need.