Like the other responder here, I too feel that his being on the autism spectrum has very little relevance, as this scenario between the two of you is no different than some of the things that happen between dating neurotypicals also.
This is just another case of two people breaking up but one person regretting that event and hoping to repair the situation, while the other person is strenuously avoiding those attempts and is done with the situation.
It's a painful and sad situation and I feel for you; it's also something that does happen a lot and can happen to anyone. Not many breakups are perfectly, calmly mutual with both parties nicely agreeing it didn't work out, take care, so long. Things CAN be that way but more of the time one person is less happy with the loss of the relationship. Heartbreak can make a person do a lot of things to win someone back, but sadly for the most part, if they're gone, they're gone.
The best thing you can do for your own peace of mind is to accept that this relationship didn't work out, and you both have to move on and chalk it up to experience. It's heartbreaking to feel like you need to win the person back but they are done with you, but sadly that's all you can do now.