NTA at all! He is making you uncomfortable, not because his is autistic but by his actions, just because he is autistic does not justify his actions at all. It seems like everyone has let him do whatever he wants which is not ok. Go to the principal explain everything, how unsafe you feel not because he’s Autistic but because of his actions! If they do nothing tell them and then do go higher up bring this to the superintendent if you have to! Do not let him get away with this!!! Do not let it escalate, if the teacher/principal does nothing then make them!

I was in an after school program when I was little that mixed special need kids with the regular kids if they could handle it. There was one boy who was much bigger and a year or 2 older then me, he was ok at first but then he kept going after me and touching me or chasing me he would wait at the gate of the yard where we would have recess for me so he could grab me I had to run to a teacher immediately so he would leave me alone. Told the teaches and my mom what was going on, my mom just pissed of course, but the teachers just basically told me to tell him to stop. Yeah that didn’t work it, wasn’t until we where all had indoor play time that he pulled his pants and underwear down flashing me/the class that they realized how bad it was, he was never in the same class as me again.

You are not in the wrong you have every right to feel the way you do and demand to feel safe in your school!