Hi bananas2,
It sounds frustrating to be stuck in more ways than one. Based upon my own small experiences, he's probably lacking in empathy, focused upon his own needs.
You sound like you're struggling with loving him; who he was, who he is, and the switch (splitting) is confusing. It concerns me that you had to leave to get away from it already. Overall, do you feel safe?
If he's recently diagnosed with BPD, that could contribute to an escalation in his emotional dysregulations. Is he in treatment? If so, how is that going?
I encourage you to take a look at the lessons to the right of this board. Understanding the illness is the first step, and the materials there can help you further, as well as the support from senior members here who are "fellow travelers," so to speak.

Turkish