From Under the Ashes

Zuko hadn't planned on becoming such a huge part of Katara's life. It just kept...happening. Somewhere along the way, she'd become this massive vortex he was incapable of avoiding. He just wanted to help the others save the next Avatar. Filling the void in Katara's heart was never part of the plan, but Aang being killed by the Phoenix King hadn't been part of the plan either.