Derek’s sniffling, and his eyes are welling up with tears, but he’s not crying yet. Make it to your room, he’s telling himself, just make it to your room. He keeps his head down, not making eye contact with anyone he passes as he speed-walks to his dorm. There’s a group of people waiting for the elevator once he gets into the building, so he veers towards the stairs, taking them two at a time up to the third floor. His hands are a little shaky as he keys into his room, but he manages to get in before sinking down to the floor, his back to the door.
He’s crying, now, silent tears running down his cheeks. He grabs his phone out of his pocket and calls the only person he wants to talk to right now.
No matter how you turn it I really believe that Katara was the most important person to Zuko after uncle Iroh. She was the one that he trusted. It was an important bond that he formed and one that went deeper than with any other individual in his life up to that point (except for Iroh ofcourse) . For a person like him that did not have any friends growing up, for someone that was not secure in himself, and was always yearning for acceptance, forming that bond was so important to him. This was also only possible because of who Katara is. She is always loving. She even was the first one that believed and accepted him from the gaang.
I also think that this something that was not acceptable for someone like Zuko. People that go through abuse have a hard time believing that there are good people. It can take a while before they put their trust into someone else. It is hard to give your heart and trust to other people if that is something that did not go well in the past. That is why their relationship is important, regardless of them being canon or not. Katara will always be the only person after uncle Iroh that he opened up to completely. Even allowing her to hurt him and getting hurt for her.