This Kataang Fanfic goes back in forth on Katara's and Aang's thought after he kissed her in episode 17 season 3 The Ember Island Players. Around the end is what I wish could have happened. Just too also clear up things, this fanfic is child readable, no high level material is in this.
Aang: I'm such an idiot! She said she was confused and that it wasn't a good time. I shouldn't have kissed her... If she actually did like me those feelings are probably long gone because of what I did. I just… I just wish I wouldn't have done that. I mean I want to kiss her, but I just wish my stubbornness wouldn't have came in the way of me waiting for a better time. Ahh… I still feel stupid… I hope she's not mad at me forever.
Katara: Why did he have to kiss me?… It's making it so much harder for me to hold in my feelings for him. I don't know what I'm going to do… I'm afraid to really let him or anyone else know how I really feel. I.. I'm afraid of letting him know that I…I…I just can't say it, if I say it I'm afraid I won't be able to stop myself from going to him and telling him how I really feel. It's just too hard with how everything is going. Sozin's Comet will be here very soon and if I let him know my true feelings and he dies then I'll feel like there's nothing left in the world. It's just so complicated…
During the play: The play has started up again and both Aang and Katara feel horrible. They both want to fix things, but they don't know how. Aang looks up to see if Katara still seems mad, but he can't tell completely. She looks like she's sad, but he's not sure.
Just then she noticed him looking and he immediately looked away. His cheeks turned red from embarrassment. He tried to hide it, but Katara still saw it, she felt really bad for what had happened. She wants to tell him, but she just can't. Looking at his innocence and his blush and knowing he cares for her more than just a friend, maybe even love her makes her so weak on holding it all in. It's killing her not to tell. Then something comes to her, if she doesn't tell him before Sozin's Comet and he dies during the fight, then he will never know how she really feels and she will feel like she lost her one chance to be with him. This caused her to shiver. She just had to tell him, and she knew when to do it.
When the play was over and most everyone agreed that the play sucked they all went to their hideout home. Once they got there Aang quickly went to hide, hoping that no one would know where he was. He felt too ashamed of himself for what he did.
Katara that night after the play planned on apologizing for how she acted and how she really felt about him. All she had to do now was find him, but as soon as they got home he ran off and disappeared. She knew, well at least had a feeling that he was still around the place so she went and checked every room, but she couldn't find him. But just when she thought that maybe it would be best to just wait until tomorrow or until he appeared she saw something on the roof. It was hard to tell from her angle, but once she got on the roof she saw him. He was mediating and trying to get his mind off of what happened earlier.
To use this to her advantage Katara quietly walked over to him, before he could run away. She sat down next to him and said his name peacefully and gently. He heard his voice called and snapped out of meditation. He was surprised that it was Katara sitting next to him. He wasn't she what to say, but he knew that he had to apologize for what had happened and that he would never try that again.
Before she could say anything more than his name he told her that he was deeply sorry for his stupidity and that he would never try anything like that again. Once he finally said that he noticed the look on Katara's face. It seemed sad from what he had said, but before he could say anymore she hugged him tightly. He was surprised, but he hugged her back. Once Katara stopped hugging him she said that it should be her that should be apologizing because she's the one that was being rude. Aang seemed confused, but Katara kept on talking. "Ever since I met you I knew something was special about you. I didn't understand what I was thinking though. At first I thought it was just because you were the avatar, but then I got to know you more and more. So I thought it was that I just had a small crush on you until the fall of Ba Sing Se, that when it hit me. When I saw you get hit by Azula's lightning I felt like a huge part of myself had died. When I had gotten you onto Appa and we were flying away I was a mess of emotions. I just couldn't handle the thought of you dying and then I remembered the spirit water and that it had special powers and I just knew that I had to try to use it on you and see if it could help. At first I thought it hadn't worked and that it was just too late, but then you started to awaken. I was so filled with pure joy to see those eyes of yours open and look at me. I felt like I was brought back to life when you were. Because of this I knew that it was just me liking you that whole time. It was that I've loved you since I first laid eyes on you. I can't live without you and I feel so horrible for not having told you sooner. I…I…just had to tell you…"
Katara was starting to tear up from admitting all of this, but it made her feel better to have a load off of her back. She noticed that Aang was tearing up to and that he was trying to tell her something. Aang finally got it out after a moment and said, "I…I…love you too…" Katara and Aang both smiled at his comment and Katara knew what she had to do. She put a hand on his cheek and leaned in to seal her lips to his. Both Aang and Katara could feel the passion of it and because of it Aang kissed her back. After a few moments of them kissing they knew by just looking at each other that they would be together forever…