He needs theo to rely on him, he needs theo to see him as his savior even when theo never needed to be saved. Jean wants to feel needed, to feel like someone needed him

He found the cute, and he hated the idea of other people having theo, jean almost has a "savior" complex, seeing Theo as someone to be saved

Despite jean's prior intentions with Theo were possesive and wanting to have a "trophy," jean over time does form some sort of "attraction" to theo (although it's brittle and more platonic than romantic). Theo is Jean's narcissistic supply.

if it makes it better or worse, this is technically a nsfw story and jean tops

i really hope to make it clear that they themselves are not toxic individuals but due to circumstances they can not control; the relationship is toxic

they are supposed to both be flawed characters that have a bitter-sweet relationship, where they both feel some sort of attraction but in the end can not work out