As they traveled together, she never thought much on their relationship. Zuko was her friend, a person whom she cared for simply because he had been adopted into her ever growing extended family.
It wasn't until he fell in battle that she realized that it was he who carried her through the tribulations they had been through; that it wasn't the fire that warmed her when she sat beside him, but the heat of his shoulder against hers. That his eyes hadn't been apathetic at all when he looked at her, but guarded so that she could not see how he truly felt.
And it wasn't until she understood how much she would lose upon his death that she realized that she was in love with him.