Need help..

Me and my boyfriend have been dating for a year but I’m worried about him and don’t know what the heck I should do. Whenever we argue he likes to self punish himself by saying things like he’s worthless, pathetic, useless etc. I’m not gonna lie ,things do get intense in our argument and I do say things I shouldn’t be saying, but I don’t think it needs to come to self punishing. He also talks about hurting himself. He hasn’t cut himself but once he threw himself down on the ground so hard his knees were bruised. He also used to hit himself. He claims he feels so helpless when we argue that’s what he results to doing. If anyone has advice please let me know.... I feel like im dating a crazy person which sucks because he really is a great guy....