It's cause he's treating our MC like some pushover. He lies about things to the MC, gets money from him, spends the money he's been given to go on dates and vacations with his other lovers.
If I remember it correctly, this guy is the MC's boyfriend, but he was cheating on him in one of the previous chapters where he confirmed that he only cares about his money and intends to leave him.
wait why do we hate this guy that's about to get killed? i can't remember but i don't feel like rereading