Find out by talking face to face..
Don't waste your time with someone that is not going to put you first.
Confront him about it, its the only way you'll find out
If I had to guess, I'd say you're smothering him.
He is breaking up with you, he just doesn't actually want to go through the act of breaking up with you therefore he is just never going to contact you and hope you take the hint.
its up to you if you want to wait for a "booty call"