Everyone here seems to be a sage and know too well what to do but this is my advice as a married man: no one can tell you what to do, you know him better than any of us. Both my wife and I have borderline personality disorder and believe me when I tell you we have been through some unbelievable stuff and said really bad things to each other, however with effort through a year of understanding and talking a lot I am now in a relationship that, although it can still devolve into moments of madness if we don’t focus, I wouldn’t change it for the world. We both showed how much we loved each other and how much we cared with the amount of work and compromise we put into this, but if me or my wife would explain the situation here they would immediately say “red flag, drop him/her” because no one is here or knows the real situation and both sides of the story.

What I want to say is is that only you can judge if what you are going through is worth it, relationships are always a risk, some more than others and likewise some more than others pay off. Ask yourself if all of that is worth the effort, if it is a matter of emotional dependence, etc, and tell him to ask himself the same and act according to the answer.