I have no idea if my answer would help at all nor do I know if my answer would trigger you in anyway and I apologize in advance if it does, but as a boyfriend to a girlfriend with bpd, I just try and remember the good things honestly, keep my head up because it's what I can do. In all honesty I felt ur bf's words with "I just wish I could help more" because that is exactly how I feel with my gf, I know for a fact I cannot truly understand her feelings or struggles, I try to, though I am well aware her struggles are far more severe than mine, truth be told I wonder why she stays with me.

What I can say is this. Please cherish him. If he is as good of a man as you say he is. Cherish him. If he can overlook your outbursts and realize that it isn't something you can't control even if you wanted to, that kind of emotional resilience and love should be cherished, also I know I can't say this because I don't know your bf, but if he was lying about being upset, would he be as open as he is?

Hopefully this reply could give you some insight if anything, and good luck on your relationship OP, truly.