I agree with what OpenEyes said about talking to him. I know it's hard if he won't reply, but I really think putting yourself out there for him to see might make him more willing to talk to you in return.

I also just want to throw out there that there could really be a million reasons why he isn't talking to you right now. And all we can do is guess and give possible reasons. He could be protecting himself from emotional hurt, afraid of getting closer to you if you don't want that in return, he could just be a jerk. He might just not know what to say to you. He could be worried that a good friendship has been ruined. It really could be soooo many different reasons. The only way to really know is to talk to him. But you probably have to really put yourself out there for him to feel comfortable if he's feeling uneasy. If he's just a jerk, then there's probably no hope. But from the sounds of it, he's probably not a jerk.

You're not alone. I've had this happen to me, though we didn't go quite as far as sex. But the reason he stopped talking to me had nothing to do with me. He was emotionally protecting himself because of factors that had nothing to do with me and that neither of us had any control over.