Why can’t I just move on?

I was talking to this guy on and off for about a month. At first we spoke everyday for a week then we were supposed to meet and he disappeared for a week. Then he started messaging again and eventually we met up 2 weeks later. We just had dinner and I went home after, we didn’t kiss or anything. We were supposed to meet again a few days later but it didn’t happen because apparently he got busy. He was still messaging me for about a week or so then he went quiet again and I haven’t heard from him for over 2 weeks apart from a random video he sent me on Instagram a few days ago but I didn’t respond coz I knew he would say it was a mistake. Anyway I just can’t get this guy out of my head, i’m constantly wondering what he’s doing, worrying what he thinks of me and hoping that he’s gonna message me. I don’t follow him on Instagram but he follows me and watches every story I post which annoys me. What Can I do to move on and forget about him, I know it’s pathetic as it was just ONE date but I can’t let it go!
Why can’t I just move on?
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