Why is he all I can think about?

He's either very shy and is intimidated of you (which is very normal) or he's trying to mess or play you! Maybe you should observe his actions and moves at school harder. If he's kinda quieter and more to himself most likely it's shyness and intimidation, so you would need to be more open to talking to him in person and starting convos and being friendly! If he's outgoing and talks to you alot or just other people (especially other girls), it might be a small chance of intimdation, but most likely he's just playing a game! You can maybe research and ask other people if he has a bad record of playing girls! Or it might be a chance of him honestly just being busy and not having time for fb or is just really lazy. Like I said don't really judge by a website too much, judge him by what he does in person! FB is honestly too overrated and is not a big deal! What kind of signs is he giving you to make you think he likes you? Make sure you reexamine them because he might just not like you! Hope this helped:)

The word "Facebook" is an invisible phrase saying "We'll ruin your relationship" lol

Take a deep breath, ask him to step aside and have a private conversation about it and come to a mutual acknowledgement that you like him a lot (maybe being friends is the best solution, for now unless he likes you too in the future).

P.S. you think about him all the time because you like him, it's just natural to do that when someone amazing comes into your life.