I'm practically in love with someone and have NO clue why??

I go to a huge high school (about 2000 kids) but there's this one guy in my sophmore grade who I've been on-off completely in love with since we were like kids and I have NO clue why. He has a nice personality but nothing special, he's average looking, and we're not even that great friends! My friends are amazed I always go back to admiring him every few months. We had a brief 'thing' this year but it never did anything. I'm honestly weirded and creeped out that I can be borderline infatuated with someone and can't even say why. I've had an on-off boyfriend I liked but he still has never overstepped the other guy. Could I be like reminded of someone ELSE or could I have dreamed of him in middle school orr what?? Lol any backup stories, science/psych facts, opinions?