Why is my ex-boyfriend doing this?!?

I know exactly how your ex feels i felt the same way with my ex :/ The fact of the matter is hes blocking you and avoiding communication from you because part of him still Loves you very much and the fact that what you guys had is over hurts him. He probably feels like things wont ever be the same between you guys and whenever he talks to you he feels all the emotion and all the memories that you guys shared together and it hurts him. Thats the reason why he keeps blocking you, he misses what he had before and still part of him loves you alot.