I don’t think it’s assault case. I doubt police would get involved. Maybe they’d advice you to move away from the stage if you feel uncomfortable

Just some ideas:
Thrusting one’s groin in that way is a common gesture for many performers

You stood very close to the stage, had a crush on him and liked his attention (it was likely noticeable) so he possibly thought you like this kind of stuff. You even tried to see them before the performance.

You were intoxicated, he was likely as well. Other people were drunk or/and high so what they said or didn’t say is irrelevant as they were not sober

You keep saying you rejected him. In which way? Did he ask you anything or even spoke to you? You never moved away no matter how badly he behaved so I don’t see you rejecting him at all. You said you refused to hang out with him in private. Did he ask to see you in private or you just think he did?

I don’t know why he sprayed water on you. It’s crazy. But I am puzzled why you still stood there?

You can never answer why people do this or that because you’ll never know but some performers love bizarre behaviors and think that fans like it (and many do, your actions showed him that you liked it so he kept on acting ridiculous).