Pls spoil for

REAL I DONT BELIEVE THAT HE FELL IN LIVE WITH HIM THERES NO WAY

it's Stockholm syndrome, and a very well-written complex depiction of it. basically, after the school arc, he has been unable to forget about his trauma and the boys. he hates them persistently, and it deteriorates his mental well-being and his life. he wants to kill them bc he cant live in the same world as them, but he's unable to kill them as they have become a permanent stain on his life which he is emotionally unable to live without. since he's unable to move on from the boys or kill them, for the sake of his survival, he chooses to love and live with them instead (atp he knows the remaining boys love him as well). anyhow there's a lot more to the story and i should mention Jerome is appalled that mc chose to forgive them, bc he himself is aware of how sickening and horrific his acts towards mc were, so he does reject and mock mc a lot for this to reignite this hatred (even tho it would mean mc wanting to kill him again). he doesn't believe mc should or can love him wholeheartedly given their history so he always tries to keep a distance from him and wont admit he loves mc even tho it's clear from his actions. honestly you just have to read the novel bc it makes sense at the end (altho i do wish there was more to jerome's "redemption")