Co-worker tries to hit on me

So I'm working as waitress and my co-worker gets sometimes way too friendly. He knows I'm in relationship and so is he, but today things get way too hairy. We were closing and drinking after hours, when he started to touch and hug me. He talked the way no doubt he tried to hit on me. I told him no many times. We were alone, because everybody else left. Eventually I left wearing my working gear because I was too afraid to change. I feel every uncomfortable, because I have to work with him. I don't want to tell the boss. Should I give notice and leave? I'm doing my internship there also.