How do I know if a boy likes me but doesn't show it?

You wouldn't know because he's hiding it lol.

If the guy likes you, you'd usually catch him looking at you, then you exchange waves, and you look down only to see him still kind of staring. Try watching him from the corner of your eye next time(without being obvious) because chances are, he's hiding it from your face but will look when you're not looking.