Guys I don't understand what that mean when He said murderer and the son why he do sex wi...

The summary above states, "Hyukjoon's son died years ago. And the one responsible for his death lives with him. Minjae isn't Hyukjoon's son. He's his target." Also, he's having sex with his friend, not his "father."

The son loves his stepdad but cant have sex with him right,so instead he have sex his friend and pretend it is his dad and the freind is into him. I think his son father must have killed his son but revenge is on boy and thats why stepfather hates his son.