Why does Ralph cry at the end of the novel?

Ralph runs into the sailor on the beach. The island is a burning inferno and the "savages" are about to kill him. The arrival of the sailor is Golding's Deus ex Machina (God in the Machine). The story has ended and Ralph contemplates everything in a moment. He finally is able to be a child again and he lets go of all his pent up frustrations and angst. He cries tears of regret and sadness rather than tears of joy. Golding puts it best when he writes, "Ralph wept for the end of innocence, the darkness of man's heart, and the fall through the air of the true, wise friend called Piggy."