How can I get him back?

For someone who gets really for long periods of time, their is really nothing you can do. That is his personality or you have done something that he's knows about but you don't know he knows and he may be very bitter about that so he picks silly things to get mad at you for to make up for the fact he can't get mad at you over whatever he is really mad at. Otherwise it's just how he is.

this may be one of the hardest things too do.
it depends though, what all have you done to him to make him mad ?
I've screwed up pretty badly with this one guy I'm still madly in love with but, he hates me.
hes very stubborn like how the guy your talking about is.

Be yourself. Do not act like someone else in order to be liked - it never works in the long run.
Don't hit on his best friend. It hurts your ex's feelings, but some people use it as revenge.
Be subtle before you try anything obvious, you need to pick up his signals first. You don't want to look desperate. Tell him you still love him. Be honest with him and yourself. Let him know you want this to work.On-and-off dating can be heart-breaking and even abusive! Always make sure that your intentions for taking him back, or vice versa, are genuine.Never forget the reason you broke up in the first place.Never let a man take advantage of you.

Wait. seriously? So you want to get a guy back who is constantly mad at you? Why in the world would you want that? You should seriously rethink that.