Guys please answer this. would you still see a girl after you hooked up with her?

i hooked up with a co worker. after IT happened, i played it cool at work the following day like nothing happened. some of our co workers would tease us that we should go out but we both just start to laugh since nobody knew we hooked up. we never talked about it. but somehow after the hook up i started to fall. as i said, i played it cool so no one suspected. sometimes he tries to get me jealous by flirting with other co workers but i usually never react. i do the same but when i do he tries to call my attention like he had something to say. lately i tried avoiding him bec i don't want him to notice, and he looks for ways to get my attention. why is that? is it because he has hooked up with me already? i often hear that once the guy gets they would lose interest in that person and everytime he gets the chance he pinches my ***.by the way, before we hooked up i told him that i wanted nothing from him. he's the 1st person i slept w/ who i wasn't involve with & he knows that.