What would you have said/done?

Last night my boyfriend borrowed his aunts car and I was annoyed for a little while because he waited to tell me last minute that he wanted to leave and then rushed me. While driving, he was being reckless and was riding the person in the front’s bumper. I yelled at him to stop and just change lanes and while it was bc I was scared we would crash, he thought I was still mad at him and wanted to fight so he yelled back. We were at his aunts by that time and he started getting really upset (he has bipolar, PTSD, and anxiety & has gone without meds because of a scheduling problem) saying he didn’t want to fight, now sobbing his eyes out.

It was a miscommunication and had we just both calmed down for a few minutes, it would have been fine. But instead his aunt decided to intervene and escalated it. She began to tell me how the problem in our relationship is that I “encourage his behavior”, that him yelling at me or being rude should be justified “because he’s not on medications atm” and the bipolar is “in his genetics”, and that making sure he gets the car back in time should be my responsibility too. I told her that I don’t “encourage him”, that him being off meds and genetically getting bipolar doesn’t mean that it make it okay, and that I was justified in being annoyed about him waiting last minute to tell me. She then proceeds to tell me that she doesn’t understand why I’m with him because I “clearly don’t understand his bipolar” and “don’t support him”. At that point my SO is having a panic attack and can’t even catch his breath.

Yet when hes talked suicidal to her she tells him not to because “she won’t let him hurt her.” I’m the one who always tries to ask about appointments, his meds, and encourages him to keep making/taking them when he tries to tell me he doesn’t want to. I don’t know how else I’m supposed to support him.