
It's the subtle hint, him searching for jin, n obsessing over him especially that five years, him restraining jin, it's not cute kinda like it's the obsessing which starts toxic kinda, well that's all I can deduce right now as a obsessed story girl. I have some other deduction which I hope is not right cuz damn i would be traumatized again! This damn manhwa is so traumatizing but addicted and amazing

It doesn't show in the story but I did find a character relationship diagram made by the author, that shows what the characters think of eachother. For Tehir towards Jin he has the following thoughts: "Hate (I love you)"
Here's the (machine translated) relationship
chart: https://i.imgur.com/hVVzrmz.jpeg

Tehir is obsessed with Jin but not because he likes him or love him. He's obsessed on making Jin experience the years of nightmare he suffered. Eye for eye sort of situation. I wouldn't call it Stockholm syndrome either. Just plain revenge that marinated for years and years. But tehir's condition doesn't allow him to actually act upon said revenge since he's always bedridden and technically only the other guy (wavy hair) take actual decisions.
Not sure here but I wonder if Jin attacked him after Tehir told him they're (the kids of the daycare) the """"chosen one"""" to which Jin laughed in one of thee previous flashback.
Maybe Jin back then attacked Tehir to prove the other that they're weren't chosen one or specials so he crippled him in a way to take away that status, but also to be on theme of his title of being "the prefect" of the group which either could mean he's both strongest and wisest of the bunch but completely lacked common sense and empathy.

Y'all I am locking this in memory. We'll come after some chapters and then let's see whose speculation is correct : one one side we have the person who read some raws and defends their hate jin. On the other side we have the guy who show the author's post n some other guy feeling guys. So who'll win ? Stay in tune to know it parampampampa

It's exactly bc of that, Tehir can't live without Jin, bc he was his last strand to sanity, he is his everything, as toxic it is, he hates him, can't live without him. Imagine thinking about only one person all day for 5 years while locked in ur own body, no matter how much u hated that person, you would feel dependent on them, bc that's what kept u sane.
Im still not sure why he likes so jin so much even though jin cause him to suffer...hmmm