I have two points to make here. For one, Jesus was sorrowful for
our sins. I make that distinction, because there seems to be a coupling of our sorrow for our sin and Jesus' sorrow. What's more, Jesus was sorrowful for His Own's rejection of Him:
He was in the world, and the world was made through him, yet the world did not know him. He came to his own, and his own people did not receive him. But to all who did receive him, who believed in his name, he gave the right to become children of God, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.
John 1:10-13
Yet Jesus was not lacking in joy. Happiness is circumstancial. Joy is present regardless of circumstances. Jesus joy was set before Him, and was in Him as He did His Father's will.