because he knows Joonie is trying his best and is cute no matter what he does and that fondness comes out when he looks at Joon being chaotic
He appreciates and admire Namjoon's leadership so much that he takes a step back so his influence stays strong while he supporte him on his side

throwback to the time he praised Namjoon's leadership skills so much Namjoon teared up

Seokjin stays by his side as he asked because Joon maybe the leader & a force to reckon withbbut he is also young dongsaeng who want his hyung by his side

Jin may never stop joking about Joon's frying pan incident but he also hangs around everytime Joon cooks to keep an eye on him
Jin will complain about Joon losing things but he find it so endearing he also calls that as Joon's hidden charm . Let's be real we all think it's cute too

when he can't help but tease clumsy Joonie because he's too cute
whenever Namjoon doubts himself Jin is there to convince him that he can do it and that there's someone who believes in him

if Joon feels like his performance wasn't great Jin will cheer him up and remind him that he did well
but the biggest way he shows his love?
its the way he insist to the world that Namjoon is amazing no matter what
its the way he insist to the world that Namjoon is amazing no matter what