How should I get over this?

Okay here goes. I have a coworker whom I was really close friends with. Overall, he's nice, but he's extremely immature and is kind of a jerk. Anyway, way back when I first started working with him, I developed a crush on him and we became friends with benefits. We've been friends with benefits on and off for the past few years. He is in a long-distance relationship and has been ever since I've known him, and recently he's been iniating ual encounters in which I would first say no and then he would keep asking and then we would go to a secret room at the office and mess around. We've never had ual , but we have played around. The last time we did this was last week and I felt unfulfilled and stupid afterwards. Then I got angry for doing this in the first place. A couple days afterwards I wrote him a note saying that the FWB is over and I wanted him to stop talking to me unless he really had to. Then I emailed him saying that if he ever asked me to play around with him that I was going to tell HR. My question is how do I deal with this. Some of my coworkers are looking at me weird or like I'm being mean. I just want him to leave me alone and I want to end any sort of friendship with this guy. The thing is how do I get over my bitterness toward him.