I yearn for someone I haven't even seen in 3 years. [conflicted]

I still think about someone who was effectively just a school crush. We sort of had a thing between the ages of 15-17, was never anything particularly serious but he was the first person I'd ever felt that way about. It all ended badly and i didn't speak to him in the last year of school. I haven't even seen him in 3 years (I'm 21) and yet I think of him regularly, I've dreamt about him most nights the past week, I check his social media frequently. Not sure why as I'd never contact him, but I guess I'm curious as to what he's up to. Not sure what I'm trying to achieve by posting this, I guess it feels like I'm not going to get over him.