Need some help in finding a BL manhwa's name

Hello, I remember reading a BL manhwa here about MC trying to take revenge on a group of rich guys who I think sa-ed his sister, who later took her life. He needed to sneak into a party reserved for members and he hooked up with ML to get him in (ML belonged to the group but did not participate in the activity).

Long story short, ML helped MC to kill them one by one (ML is a psycho and finds pleasure in killing) MC stopped him when they started dating officially by giving ML a deadline of a few years. ML indeed stopped and worked as a forensic if I remember correctly. At the end of the manhwa, the deadline was up and it was heavily emphasised that ML would be starting his killing spree again.

I cannot remember the name of the manhwa, anyone knows? Please let me know. I wanna read it again hehe