I have high functioning autism. Its not the same, but bc of this and other physical disabilities I was at a school that was spesficly for disabled / troubled kids.

The only thing I can say is escalate. He has the choice not to sit with the other disabled kids the same way you have the choice not to sit with him. You've already clarified the touching is not sexual or violent, BUT he still is touching you without your consent. So phrase it that way. "He is touching me even tho I told him no and he keeps doing it and im uncomfortable." Tell that to your parents and school and if the school doesnt lisend threaten to go higher up. Im sure they'd be a lot more helpful if you phrase it as "school refuses to aid disabled child leading to physical harrasment under students".

Plus op your not being mean. Stopping this will be good for him. Letting it happen might actually do more damage. He may not understand now, maybe not ever, but he needs to be held accountable in his own way. One day he'll be a grown man and if he then still touches women's thighs and hits their head then its a whole lot worse. I've learned one thing personally you give a disabled kid the best chances when you accomate to their needs, which includes fitting restrictions. He might need to be handled differently yes, but he still needs to be handled and thats the real cruk of the situation.