Because they had more sex scenes and the extreme codependency they have. I don't really care about this work's ships but the thing with TJ and Ian is that their relationship is toxic. What they have goes beyond love. They probably wouldn't be happy or at peace together because TJ is never leaving the gang and he wants to drag Ian with him, to those "happy times" when Ian just waited for him in a corner. He wanted a whole house to live with Ian there because he thought that would make Ian happy and content, even if that's not Ian's style.
TJ always decides for both of them because he seems to considers Ian's sudden actions a problem to his plans for their "happy ending". But manly because he needs to control everything, even Ian. TJ pierced Ian's earlobes, not remeber if both of them, give him earrings like his and put a chain on him like the one he have. Marks of ownership.
He 'let' Ian have one night stands because they never stayed and Ian is always at his call in the end. But everything changed with Jo.
Ian loves him, TJ is obsessed with him, but they have a mutual understanding of their situation. Still I'm pretty sure Ian will try to escape from time to time because he doesn't want that kind of life anymore. He doesn't want the killing, the hiding, the danger... Ian wants an unrealistic dream life with TJ where they can live like normal people. When Ian met Jo, Ian started wanting more of life. He wants what he have with Jo but with Ian.
It's pretty messed up and Ian won't leave TJ. But I don't think he's confused about what he want anymore. Still TJ will always be important to him. Their bond is like a chain that weights on him and Ian doesn't have it in him to be free tbh.
So I get why people confuse that with love.
* "He wants what he have with Jo but with TJ."
I made a mistake hahaha
u literally summarized it so perfectly u ate
i just don’t understand how yall still want tj with ian after all that’s happened