It seems like this was maybe not an ideal situation for you to be in, but also that at any point you could have walked away.
Were you physically incapacitated? Unable to walk? Semi-lucid?

Did he use social influence or threatening behavior to get you to drink or use drugs? Did you ever explicitly deny consent for any of the touching? Did you explicitly consent to any touching? Or do touching of your own? Did you signal that you were intoxicated to the point of not being able to consent? Did you signal, in the moment, that you were enjoying yourself?

Humans still have a responsibility to take care in social situations. What did you do that could have signalled you were going along with his advances? What opportunities to leave, sober up, or change activities did you take?

Please talk to this person and make your feelings clear.