hi Jon, and
so, the key is understanding and realistic expectations.
recovery from BPD tends to be a long, bumpy road. that can involve lots of starts and stops, or "relapses". these can often take place at times where some of the greatest progress seems evident.
so in general, her breaking things off for now isnt terribly surprising, and there most definitely is hope.
for a romantic partner, its important to assess the role of emotional caretaker, and those realistic expectations. this article was written for parents, about children, but it gives a very good idea of how to approach this:
https://bpdfamily.com/content/support-child-therapyso, how long have the two of you been together? how have things been going since she left therapy? whats going on now?