"I really think she does, Aang," he agrees, but there's a complex look of conflicted pain growing on his face. "But if she wants to just be my sister, then our mother has everything to do with that, too."

This is all so much to process at once. Aang being here at all, trying to convince him to trust Zuko's judgment to trust Azula (because convincing him to trust Azula himself is out of the question), explaining time and space travel, finding out about their mother, all of it at once... Of course it hurts.