I know we're not supposed to say "end things" but if he already did that, I'm not sure where this falls.
What I would do is focus on the immediate issue of the lease/co-habitation.
If you really can't get out of it, maybe you could calmly ask him to have his therapist help him create a list of boundaries and expectations for the duration of your cohabitation that are reasonable enough for you both to get through the next couple of months without additional pain.
If he in fact has BPD, he will hopefully calm down and stop being so verbally abusive toward you. Considering the "self-diagnosis", I can't help but feel skeptical.
Those of us who love or have loved someone with an actual diagnosis don't find it any easier to take the hurtful words they throw out during certain stages.
I really hope you are fully aware that the negative things he's saying are not a reflection of you at all. I'm sorry you're going through this.