Zuko's honor had always depended on the Avatar.
At first, it was his capture no matter what the cost, no matter who or what he had to hurt or destroy in his search. (thirteen years old, freshly banished and scarred and shamed for his pitiful weakness)
"Even if it takes me until my dying day, I will capture the Avatar and regain my honor." (completely obsessed with the boy to the point where even he wondered how healthy it was)
When the Avatar was thought to be dead, no longer a threat to the Fire Nation's victory, he'd won his father's love and admiration. The perfect prince.
"But I wasn't myself." (everything Iroh taught him, the chance he'd thrown away in the Crystal Catacombs, Aang's near-death)
He finally revealed the truth to his father on the day of the eclipse, throwing away one redemption for another.
"It's the Avatar's destiny to end you, and mine to help him!" (his father's shock, anger, and finally fear as his attempt on Zuko's life failed, throwing him back against the wall of his throne room)
His struggle to gain acceptance among the group was hard, and he found himself longing for Aang's acceptance more than he'd ever longed for his father's.
"We can't trust you...I can't trust you after all you've done to us, Zuko!" (words stinging a thousand times more than his father or Azula's harshest rebukes)
He remembers the day they finally became friends, and how quickly it blossomed into so much more. (their dance completed, their training finished for the day, he feels Aang's lips shyly press against his)
They lie together within the confines of their tent after saying goodnight to the others; Sokka and Suki can't get rid of them fast enough, Toph can't drag Katara away fast enough. That's just fine with Zuko.
"It was once my life's purpose to track you down, but now it's to walk beside you." (pressing a chaste kiss to Aang's lips, the smaller, lithe body warm and comforting against his own)
Zuko's honor would always depend on the Avatar.