Harassed by coworker, Anon

I am married and the man who assaulted me is also married, has a child (who attends our kindergarten), and he is also my coworker.
The staff was at a work party celebrating completing the first month of school. The man was speaking to myself and a couple other coworkers about Tinder and how “awesome” it was. About how if he was single he’d be “fucking a young woman every night!” He also expressed that he wanted to be on it; when I said, “yah, if you weren’t married” he responded with “well, we all do stuff”. He then (sitting next to me) slurs out “are you on Tinder?” (Side note; everyone knows I am maried, also my husband was at this event). I say that I am happily married. He asks against and I say firmly, “No”. during this whole conversation he is staring down my shirt: in a very obvious way. He then get up to get another drink, pushes himself up against me from behind, with his hands on my hips, and whispers in a slurred, drunken voice, “I really want to dance with you later”. He ran his hands down my lower back, slapped my ass, and walked away to get his drink. I left the bar right after that; my husband got me out safely and quickly. I was very upset; this was the fourth time I have been assaulted… (Different men).
I reported it to my school and went through a week of having to have a meeting everyday (going through every detail over and over). Including a meeting where he was in the room. His story changed several times, and mine stayed consistent, yet the admin decided to take no action against him: he still works with me. I got labeled as overreacting and over sensitive.
I was told by a female coworker that I should have talked to the man personally for clarification before reporting it. I heard “he was drunk” “he was just being friendly” and “are you sure that’s what happened?”
I go to counselling to deal with my anxiety now. It’s very hard working with him everyday. I try not to let my students near him…