he tried to cheat and I can’t move on 😭

I’ve been with my boyfriend for nine months now, and I still can’t get over what happened. I need help on trying to move on because the thought of this happening still haunts me and makes me physically sick to this day. This is what happened

My boyfriend asked me to be official 3 days before new year. I said yes. I went away to another city for new year and one of his friends had a party. While at the party baring it mind he just asked me out and promised me he wouldn’t do drugs. Him and a girl were on their way to a bank to take out money for drugs off of HIS card when he tried to make out with her and get her to grope him IN AN ALLEYWAY! Coming from the girl she said she stopped him because he had just asked me out but I will never know if she stopped or not. That night he also told his friends I was depressed and had self harmed, he also ignored me most the night but continued to post photos of him and his ex on his story. He then lied to me until I found out from her friend 4 months AFTER it happened. It’s now been 5 months since I found out and I can’t get it out of my head 😣😣 I don’t know if I can move on it hurts so much please