The boy was crying now. Not that there was any new or sudden sorrow. There just seemed to be nothing else to fill up the vast lostness of the moment.

The boy is so bereft at the loss of his father and dog in Chapter 3 that he cannot think of anything else to do other than cry. He has searched for his dog to no avail—he has wished and prayed and nothing has filled the loneliness or brought his father or dog back to him. The only thing he can think to do to fill the loneliness and emptiness is to put his tears in it. This quote shows how little the boy really has and what little solace and comfort is available to him.