Well, sometimes they might have a dreamy look on their faces, so that tells you that the boy likes the girl. Or maybe sometimes he can't stop thinking about her...like her hair, or her pretty face, or butt...boys can be weird.
He will talk about them all the time, and will accidently say her name or something. He will notice small things about her, and not make her feel jealous at all. Not even LOOK at other girls!
