You're not the asshole.
Ghosting someone you've had a real relationship with is always an asshole move (barring extraordinary circumstances, like abusive relationships).
But this is more complicated than most situations due to the nature of your relationship.
Some things to consider:
He may genuinely be stressed/busy/etc and not actually avoiding you, and/or
He may not know what to do with you.
Clearly you like each other, but it also sounds like you may not be good for each other as romantic partners. If so, he may be in a weird situation where he really likes you but also knows that having a serious relationship with you isn't a good idea ... that's hard for anyone to handle elegantly.
Throw in the recent kissing leading up to this, as well as the fact that he actually replied to you without taking the easy out you gave him...
I'm inclined to think scenario 2 is the bigger factor here, based on the facts given.
If so, you can't do much except let him work it out - and communications or advances from you (texts, calls, whatever - no matter how lighthearted) may make him feel more pressured or stressed (which would make it easier for him to walk away).
If you think it is appropriate under the circumstances, you might consider sending him a single, short message letting him know you understand and are happy to hear from him when he's settled down -- ultra short, sweet, low-key, just so that your last communication isn't an angry one and the door is open.
Of course, this is all WILD speculation on my part and could be completely off base. Hope it works out :)