Why am I stuck on him

There’s this guy I always had a crush on throughout high school. We talked a little bit didn’t go far. One day I caught my bf cheating and broke up with him. I guess I was looking to feel validated. I hit this guy up and we had sex. I told him it wouldn’t happen again but somehow I became infatuated with him. He took it for what it was, just a hook up. One day I drank too much and blew up his phone and he did not respond. He stopped hitting me up after that. It drove me crazy. I apologized to him we hooked up one other time. He did not really message me after that. I feel like I killed it for him. I asked him why he stopped talking to me and he said because it was only a hook up and I was making things too deep. I accepted it and stopped talking to him for months. I haven’t stopped thinking about him or looking at his social media. I drunk called him the other night for a ride he said no. I feel like I keep digging myself into a deeper and deeper hole with him. I want to reach out to him but I feel like it will only make it worse. I don’t know why I can’t move past this guy?!! It’s driving me insane. He obviously doesn’t like me but why am I obsessed with him and how do I get over him?