Hey InDespair, welcome. Glad you reached out for more support and understanding -- I hear in what you wrote that sense of absolute shock at your BF "turning against you" and blaming you for behaviors, at a time when you were actually reaching out to him needing compassion.
The first thing I thought of when I read your post was the concept of "splitting", where many pwBPD struggle to allow people (and situations) to just be gray areas -- things have to be good OR bad, black OR white, and nothing in between. Additionally, many pwBPD struggle to support others who need help, including emotional help, listening, all that stuff that we think of as "normal" in a relationship.
So, one idea for what may have happened with your BF could be:
While he had some baseline skills (he was initially able to talk about not letting those words get to you), he rapidly hit his limit with his ability to be emotionally supportive. Feeling anxious, overwhelmed, etc, and possibly having an "external locus of control" that many pwBPD have (the mindset that "my feelings come from outside of me and are caused by others, and also are factually true"), he may have seen you as the source of his anxiety/overwhelm. If you are around, and he has bad feelings... well, according to BPD, you are making him feel that way and are therefore bad.
Thus, he could pivot pretty quickly from "I am here for you" to "you are the problem" to "if you're the problem, you are bad and do bad things like XYZ".
If you haven't seen it yet, you could take a look at our workshop on
BEHAVIORS: Splitting, and let us know if any of it resonates with you.
Ultimately, I think you're on to something here:
So I don't know, maybe this instance I brought up to him and my constant being sad about us being apart was just too much for him now?
It could be that he has some emotional support limitations that are a lot more limited than you'd want or had expected. That being said, learning more about how BPD impacts people can help you understand those limitations and try some different tools and skills to see if you can personally make changes that make your relationship more livable.
Write back whenever works for you;
kells76