He needs some space
Remember when we said that everyone is different, well this point kind of follows on from that.
Let's use that same example again - you love to text all day, he likes to save all the chatting for the evening when you see each other. If you don't talk to him about this and keep on texting him, then leave him voicemails asking why he hasn't text back, then write messages on his Facebook wall, you can imagine that he might start to need a bit of space.
Again, it doesn't mean that he doesn't like you, it might be simply that he needs some time to himself.
He also needs time to miss you, that way he'll really look forward to seeing you.