Why do you think that the pensioner cried during the fifth year of his captivity?

We are not told about the fifth year specifically, although we can infer that he was feeling remorse over his decision and suffering from depression.

In the second year the piano was silent in the lodge, and the prisoner asked only for the classics. In the fifth year music was audible again, and the prisoner asked for wine. Those who watched him through the window said that all that year he spent doing nothing but eating and drinking and lying on his bed, frequently yawning and angrily talking to himself. He did not read books. Sometimes at night he would sit down to write; he would spend hours writing, and in the morning tear up all that he had written. More than once he could be heard crying.