Sokka is the first to notice Zuko's loss of vision on the left
He approached him once in classic Sokka fashion, loud and annoying and with complete lack of respect for personal space
Zuko tried not to flinch too obviously but Sokka noticed anyway, ofc
Since then he always comes from the right
When he has to be at his left, he announces himself even more loudly than usual
No one else noticed much difference, but Zuko does
He's been waiting for the other shoe to drop ever since Sokka found about about his eye
He's expecting threats or weakness being taken an advantage of or other such plans as would be expected by the strategist of the team
He has no idea what to do with polite accommodation and normalcy
This continues while they're still not quite trusting each other, still figuring stuff out
Sokka remains respectful and knows it makes Zuko nervous to have anyone he doesn't trust on his left
This little fact is what changes everything at the Boiling Rock
At the temple, there isn't constant threat to Zuko. Sokka then can afford to be careful of the guy's boundaries, and he's not necessarily the closest to him either
But at the prison suddenly they're surrounded by hostile people everywhere
Sokka sticks to Zuko's left whenever they're together
Zuko notices, and by now he's at least realised that normal people trying to be his friends wouldn't use a weakness against him
He stopped expecting Sokka to turn on him a while ago, but here he notices what the strategist of the group actually does with knowing his team's weaknesses
He protects them, maybe even subconsciously
Sokka knows Zuko needs the reassurance, and he's always there, at his left
When they fight together, they fit into a rhythm unthinkingly, and from then on Sokka is always at his left
Zuko doesn't quite know what it's like to feel safe, but when Sokka is next to him, guarding his greatest insecurity, he thinks maybe he's learning
Sokka sits at his left in meetings with war hungry generals
Sokka still announces himself when coming to him from the left
When they start dating, it gets worse (better)
Sokka always has a hand or arm on or around him, and he's always on the left
Zuko thinks maybe he'll forget what it felt like for his left side to not feel safe
Now it's entirely just Sokka's space