I think that if Jihyun’s character had some character development he would’ve ended up with Chiwoo, but his personality didn’t just come from any where. He was abused at home and neglected, so it was like understandable that he was afraid that Chiwoo would left him (which he did at the end).
Jihyun’s character was not toxic, growing up in a family like that, you can’t avoid having trauma, although he had someone by his side, he would still long for his family’s love..
So his reactions from being ignored or when he was feeling that he would be left behind, was to stop them to, by violence (that he get from home).....
Back to School: All Grown Up