i reread it from the beginning and idk... their progression has always been like that, definitely not comrades or bros but partners who love eachother.
they don't express it as aggressively as mo and he tian since they're much more subtle and not big into pda... even in chapter 476 they go around a corner away from the public so be romantic in private
yeah idk if i really feel the same, i can remember two times they kiss, in the beginning they have a really cute moment where jian yi tells zhangxi he likes him and he replies with 'i know.'
they have many emotional moments, and zhangxi is always drops everything to save or help jian yi. honestly their storyline peaked when jian yi learns that his father had died and zhangxi is there to comfort him- and now their stories are cute and funny moments.
maybe you should reread if you feel like it's lacking
Jian Yi & Zhan Zengxi are too wholesome & pure for this world, & that's ignoring the 200 times Yi has dry-humped Zhengxi's leg, grabbed his ass, removed his pants, or pinned him to a wall or bed.
Zeng-Xi has softened. He rarely hits Jian Yi for anything anymore, he blushes whenJian Yi is naked or the sexy photo he did for band club, he has plans to buy an apartment for Jian Yi & himself that he wants to pay for by himself, he gave Jian Yi a ring for Valentines day, they frequently sleep in the same bed albiet clothed, & he rarely acts like a tsundere when Jian Yi flirts with him. He generally just does whatever Jian Yi wants without question while acting like a knight protecting a very crass & impish princess. Legit thinking Zheng-Xi is on the asexual spectrum & trying to build up the courage to commit physically, or he's saving himself for the honeymoon.

Damn it... The author's so cruel... Why give us those snippets/merch of xixi and jian yi as a couple if after all this time there's still no progress? Like... It's not even edging cuz they really just feel like they're acquaintances or comrades or bros (ノಠ益ಠ)ノ彡┻━┻ರ╭╮ರ