I agree ~ men & women don't really understand each other.
He quite likes you.
You like him.
You give him your number.
He thinks ~
What should I say? What should I do? What does she expect?
(Have you read the problems on here from young men asking what to say & how to behave?!?!)
So he frets and thinks, and then he thinks he's left it too late. Maybe he thinks that he has offended you.
You aren't contacting him any more and he doesn't know how to start up a conversation again. Etc, etc.
If he hadn't been friendly in the first place, I'd say he wasn't interested, but, since he was, I'd say that he might just be confused about what to do and what you want.
It's also possible, I suppose, that he's wondering if you just give out your number to boys on a regular basis???
I think that, once again, you have to make the move. Maybe, as Sal says, explain or apologise, or anything to get the conversation flowing naturally again.
He may be shy ~ and really nice ~ and worth a little extra time and work.