My boyfriend and I have been dating for around 6 months both early 20s , when we I totally started dating he told me he had some mental health issues. It had them all under wraps but I should be aware (at the time it was presumed schizophrenia) but in recent months his mental health started to play up and I encouraged him to seek help and he has been presumed to have bpd and is hoping to start seeing a therapist soon.
This month he has seemingly been okay and had very little issues but last night whilst ordering a takeaway a group of drunk lads started saying derogatory things towards me, joking about having sec with me and commenting on my appearance in an all around weird way. I kept my head down but he interacted with them telling them to fuck off which only made them comment more and no matter how much I told him to stop he didn’t. When the lads left he lost it he was squeezing my hand so tight I couldn’t feel it whilst muttering vivid ways he’d murder them. I’ve seen him have episodes but nothing like this when we got outside he threw one of the cans of coke and stomped on it before snapping the face mask I’d let him borrow, still saying ways he’d kill them. 
I didn’t know what to do I couldn’t leave him so I attempted to get him home as he lives round the corner but when he shouted his name he ran off until he got to a bus stop and sat down crying still saying things. I walked up to him and sat next to him told him I wasn’t mad I just needed to get him home and hugged him. He calmed down just enough to get home but was still so angry and seeing things. When we got home he’d go from crying to anger to hugging me apologizing.

I would never blame him or be mad at him over this but I need to know if there’s a way we can both deal with this healthily because if he was alone idk if he’d still be here with how he was.
Sorry for the length of this thank you :)