It's Lo'ak and Ao'nung in the red string of fate universe just warning you.
But imagine this, only humans have a red string of fate. Jake still had his when he entered his Na'vi body which messed with him for awhile because was Neytiri for him or Tommy???
Anyway, only Jake's kids with five fingers have the string, not Neteyam and not Tuk. Kiri and Lo'ak both asked about their red-string when it appeared when they turned five. Jake explained how it work, and also explain to Spider cause he had a red string as well.
Years down the line, when the Sully's get to the Metkayina tribe, Lo'ak sees his string ending. He's thrilled! For a moment, he think it leads to Tsireya, but she moves as her brother comes by her side...and surprise surprise his string is tied to Ao'nung. He's fine with it in the beginning, however, then Ao'nung starts making those asshole comments and Lo'ak is already done with this guy.
Cue the scene with the fistfight and Lo'ak later tells his Dad that he found the end of his string, he's just a dick. Jake tells him to apologize and what not, but then Ao'nung invites Lo'ak to go hunting with them.
Lo'ak getting all kinds of twisty feelings in his gut, cause oh, maybe the string is right. The ONLY reason Lo'ak agreed was because he thought Ao'nung was actually trying to be nice, like the string fated them to be.
Whomp Whomp, he is still left out in the ocean.
Now he's a wet, upset cat with a broken heart.
IDK where to take it from there, but like, I was thinking about the movie again, and I was like, Lo'ak, c'mon, have some sense. You're better than this. Then the thought struck me.