I've known him for about two years total, but during that time span, he ignored me multiple times for weeks to months. I can usually feel when they're coming on because he always has his cell phone on him, checking for texts, and when I don't receive replies back in a day (usually I'll receive replies within a couple of minutes), I text him. Sometimes if I send consecutive texts, he'd snap at me before ignoring me. Other times, he'll just start the silent treatment without a word for no apparent reason.
We went through a dating phase, but it never fully evolved into a relationship. He became hypersexual (to the point where it was clearly not normal), and things almost devolved to a fwb relationship.
It would be all good and dandy if he ignored me and left it at that, but he would always come back like nothing happened. There would be a few good weeks, and then back to stonewalling again. Last time, he even blocked me on Facebook.
At some point in the past couple of months, without my knowing, he unblocked me and wished me a happy birthday. After nearly five months of silence. We decided that we could try to reconnect, and he said he didn't know where to go from there. Then--silence.
Every time he does this, it throws my mind for a loop, and I'm back to the same feelings I tried so hard to work through in the past when he ignored me. This time, I'm ashamed to say that I sent him a barrage of texts about how he hurt me but I was willing to try talking again. He's conditioned me so much to his silent treatment episodes that it's become almost a compulsion to text him when he refuses to respond.
He then re-blocked me on Facebook. I sent him a text to apologize for freaking out. No response. Calls, e-mails, texts--ignored. If he tells me he needs time to think or he's confused, etc. I'd listen, but he's not saying ANYTHING. I reached out to a mutual friend to contact him, letting him know I am sorry and would also like to reconnect. He deactivates his entire Facebook account. He hasn't gone this far in the past, which worries me.
Why is he so afraid to say anything? I'm very worried about him and want to be able to be a good friend. He's told me before that he's cut off/stopped talking to friends and even family members, has a short temper, holds grudges, etc. He would even tell me about what jerks some of his CURRENT friends are, and he dislikes almost all of his friends' significant others. Yet in front of him, he's the most polite, soft-spoken person ever. When we actually see each other in person, everything's cool, and we get along fabulously, though sometimes I would notice that he'd zone out to the tv or masturbate or sleep to put things off like schoolwork, etc. He would get upset when friends ignored him--or what he perceived as them ignoring him (he never reached out to them, either), so I want to be there for him because I don't want him to be upset, but he must be upset now when I'm NOT ignoring him.

I'm almost at the end of my rope here. Has anyone dealt with extreme silent treatments like this before? Any other person would have replied or told me to stop by now.
