Hello.

I can relate to your partner’s behavior.I get upset easily and when I’m really angry I say hurtful things to my boyfriend and become distant because I just want him to feel what I feel. Those things are not true but in that moment I feel they are (even if I know they aren’t!).
Maybe your partner feels really hurt and know no other way to deal with that anger. Now I see how much this kind of behavior really affects other people.
You got back together after 5 months, that means you really love each other. It’s hard to deal with a person who can’t control his own feelings and I don’t think there is something you can do about it. He has to change or at least try to be more understanding and calm (which I know from my own experience it’s pretty damn hard).
I don’t know your situation, all I can do is talk from my experience. I think all you can do is give him an ultimatum, but make sure he understands you’re really serious about it and he can’t change your mind if he doesn’t do what you ask him ( for example: stop saying those hurtful things). Make sure he also understands how much his behavior hurts you.