If jinsol explained his situation and asked for help..
Then
Saegye would have exchanged his dare for a short period of time..
I agree that would make way more sense if he can tell the truth through writing. I guess you could justify it by saying Jinsol didn't know or trust Saegye yet. All he'd seen was a guy who cheats on tests and lies to take smoke breaks. Not exactly projecting a selfless do-gooder image.
By the time he made Saegye fall for him he also saw Saegye abandon someone he loved to preserve his own safety, too. It was less risky to lie.
If MC was alive Fabian would made his life hell.. Fabian could do anything to his family..
If MC killed Fabian then he won't be able to see Fabian suffer for long
To make Fabian suffer for his whole life and to crush his ego he killed himself..
According to me it was good decision..
I would have killed, this jerk won’t suffer he will forget everything within a month or two and find another victim.
But then again the MC was mafia most likely he would be in jail forever, so that was a wise deicision