I think it would be funny if the "situationship" between Jet and Zuko was comical, and if Aang found out about it.
"I'm the Avatar, and I have problems with a lot of people a lot of the time, but I'll always have that 'situationship' with you, and I wouldn't trade you for anyone, but sure, you can have other 'situationships' and fight with other guys"
But how would Aang feel after what happened in Ba Sing Se? And when Zuko came along wanting to join him (I want drama)?
(I don't know, I just wish that every time they saw each other, like in Book Two, Aang would compliment Zuko, like, I don't know, "Wow, I love your new look, sweetie! Your hair is growing in very pretty!" or "Green really suits you really good, it brings out your eyes")
Yeah no I can definitely see there being a little jealousy going on if Aang ever found out about the whole toxic, doomed situationship Jet and Zuko had going on, and honestly that gave me some inspiration for some dialogue I've already written for them about "favourite enemies" and all that. It's also on my list of things I need to draw for this AU lmao.
Honestly though, one thing I ran into when deciding to age Aang up is that he's hella charismatic, and he's someone who could have chemistry with pretty much anyone. So I'm asking you to consider Aang having his very own weird thing going on with Jet. Nothing too serious, I just don't think it would be too out of character for this version of Aang to have a small crush on him, especially this early on (It's before his flirting with Zuko would become more serious anyway). Idk, if I ever wrote a fic about this I'd have to give Aang something to do during the freedomfighters episode, so why not you know? Katara and Jet would still be more prominent, but I think it would be fun to throw that into the mix as it solves the issue of why an older Aang wouldn't back Sokka here. As an added bonus, Sokka would get to endlessly make fun of Aangs absolute rancid taste in men because it would NOT look good for him at this point.
OH what you're wishing for in Book Two is what I'm imagining myself, I mean they did make out at the North Pole so. Aang is definitely amping up the flirting whenever he sees him. He's definitely not the smoothest though, I'm never forgetting "It's a compliment! I'm saying I'd rather kiss you than die!" and I'm gonna incorporate that vibe one way or another. I know I've kinda portrayed him as a bit more suave until this point, but I imagine that it's easier when there's no real feelings there yet. Post the Blue Spirit and the North Pole he's kinda awkward about Zuko, both when he's around or comes up in conversation. He's still "successful" at flirting the majority of the time, he's just a bit more prone to put his foot in his mouth now. Zuko wants to die about it, nothing new there.
Ok over to the drama, I've been toying with the idea of making them date a bit in Ba Sing Se just to add even more shit to Aangs terrible, horrible, no good, very bad year from hell. Not only did he die, feel like he let the entire world down, and lose access to the avatar state, the boy he really likes quite literally backstabbed him the first chance he got. It's heartbreaking, embarrassing, and who could he even talk about this with? I was also thinking it could be an interesting character moment here, as I'd like to incorporate some of Aangs tendency to flee when things get "real" into his personal relationships one way or another, be it in a flashback to his life before getting frozen or something else. It's honestly just an extension of his fear of isolation and being erased in favour of being seen as the Avatar. I'd just like to emphasize that him voluntarily getting close to Zuko and wanting to see where things go is a pretty big deal for him. Only to have it confirmed immediately that all his fears and insecurities were true after all, Zuko only ever saw him as the avatar, and he's doomed to always be alone. After he runs away at the start of Book Three he'd come to his senses and talk to Katara, who'd knock some sense into him. Cause she gets it (Jet, love how he haunts the narrative here. And of course, she also feels betrayed by Zuko. Katara and Aang will hardcore bond in book three). Obviously this will not make things easier for Zuko when he tries to join them. ANYWAY, Aang would go back to normal-ish, but that fear of abandonment and distrust would shine through. I think he'd try to stay positive, but with a slight edge that wasn't there before.
As for Aangs reaction to Zuko trying to join them? Can I get an oof? Now, Aang isn't the type of character to hold grudges, and I think that's true here as well. Doesn't mean he'll forget what Zuko did though, he'd definitely hold him at an arms length for a while. He'll not be as explicit in his distrust and hurt as Katara, but there won't be any flirty comments from him anymore. Zuko will have to work really hard during their roadtrip is what I'm saying. I just really like to turn their dynamic a bit on its head here, cause Aang was the one trying to get Zuko to open up during Book one and two, but now Zuko will have to return the favour :) But yeah, their roadtrip ends with them trying to start again with clean slates, like they wouldn't define anything yet but they're absolutely going to be insufferable together.
Katara does not approve of this relationship, and can you blame her? She's seeing her best friend get back together with his toxic ex who broke his heart, and after they talked shit about him together too :/