Hi emp4th, that's all very hurtful and I am sorry you got hurt.
A couple of things - You didn't Cause it, can't Control it and can't Cure it (whatever is wrong with him and it sounds like a lot more than weed and gambling). So those are the 3 C's.
Secondly, have you ever read a book called Codependent No More by Melody Beattie? It is very often recommended here and talks a lot about boundaries in relationships etc, it would probably be a good idea to read that if you want to.
He sounds pretty horrible really? He treats you poorly, he is more interested in partying and drugs than anything else. He has verbally abused you and he's mean.
What exactly do you see in him. Is this really a relationship you want? The fact you have been in 2 relationships, by the time you are 22, that both involved addictions is a red flag, for you.
He doesn't sound like a nice guy or that he is in any way ready for a relationship. You deserve to be treated with kindness and respect, that is something he can't offer.
It hurts, even when it wasn't a great relationship. Do you really think you made a mistake breaking up with him or do you think that perhaps by contacting him again it would help to solve the hurt? It won't you know, he hasn't changed at all, he won't treat you any better. It will take time to heal from this, many months probably. The best thing to do is focus back on yourself. What do you want, what is fun for you? Spend time with family and friends that care about you.