What do you do when a guy kisses you when you both have a significant other?

He almost kissed me before but he didn't, and he flirts. I was hanging out with him who's 3 or 4 years older than me. He called me a friend with benefits the night before. We were talking and he was holding me around the waist and out of NO WHERE he was making out with me (do note i wasn't kissing back). When we pulled away he said I was shaking and my eyes were wide. All I said was "Holy S**t" and then he sat me down on a log (we were in the woods) and when he left he kissed me again and LEFT ME THERE!!!!