Why does this happens?

I’ve been dreaming about a guy I met almos 8-9 years ago, he was my neighbor until last year, we met in high school just for one year (we just shared classes one year). I always liked him and he liked me back, we weren’t friends but we liked each other -actually, his friends always said he has a crush on me.
For these 8-9 years, I never forgot him. I got to know TONS of guys, had a crush on a few of them but still i never forgot about this guy.
The question is, why sometimes randomly he is in my dreams? I don’t think about him until he appears in my dreams. It’s strange because even though I met tons of people and guys, I just can’t forget him. Does it mean that he thought about me and that’s why he’s in my dream, like telepathy? Why couldn’t I forget him?
Why does this happens?
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