If you've told him lots of times and things haven't changed, it could a classic case of Aspie shutdowns to me. If that's what it is at the end of the day, he's not ignoring you - he's just taking time to recharge from all the social interaction he endures. It isn't something he can control and, therefore, is something that needs to be accepted. The more you talk to him during these periods trying to get an answer out of him, the more you push him away. You need to give him that space to recharge, uninterrupted no matter how long that time period.
As well, Mindslave's point checks out - you're in a friends with benefits with him. You're technically not in a committed relationship, so he shouldn't really be expected to up the communication unless you're both planning on boosting it to a relationship. Going from that angle, if you want more commitment from him, you might have to talk to him about making you two official.
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I don't seek to be popular
I seek to be well-known
If we find a friendship that's forged without masks
Then I have done my job