HELP! Falling for a hook up

How do I stop this shit? Me and this guy only had sex like, 3 times. But I can't stop thinking of him. He'll only text me late at night when he wants to fuck. He's 37 and I'm 19. I think about him constantly and been taking extra pain killers at night so I can fall asleep and not think of him. I'm so scared because I'm so much younger and not that expert in this kind of situations. He's a nice person, treats me right and was never disrespectful to me, but I feel like every time we see each other I fall a little bit more for him. I've tried everything, deleting his phone number & our old texts from my phone and stopped following his posts on Facebook so I'd think less about him but it doesn't seem to help. Anyone has ever been on my shoes? What did you do?