Why does Ralph cry at the end of the novel?

"Ralph wept for the end of innocence, darkness of man's heart, and the fall through the air of the true wise friend Piggy"

I suppose I should elaborate a little. Ralph is no longer a boy. Although he is probably still the same age as when he hit the island, he has seen and experienced too much to go back to being a child. Ralph realizes the inherent evil in mans' heart. The boys go from simply being annoying to being down right evil. Finally Ralph realizes that Piggy was more than the offensive moniker that people had given him. Ironically we never really find out his real name but he was really a true friend to Ralph.