help??

So partner and I were having an argument, he completely lost it so I went outside so I didn't say anything hurtful and told him to stay inside. He started smashing stuff (things I made for v day) and went and cried in our bedroom. I went inside after him crying to see a knife and to see he had cut himself and, i asked why he did it and he said that because I had done in the past (way before I even met him) he thought he had every right to join the club and if everyone else can then why can't he? I got him to calm down and take a shower and cleaned up the cuts, he's now in bed asleep. But what the hell do I do? The argument was because he had a dig at me smoking and then I decided to ignore him because he hurt my feelings and he just erupted and went crazy, yelling and carrying on saying I was mentally abusing him and started throwing my stuff around and waving his hands in my face asking why I thought I was better than him when I was literally sitting there doing nothing.