Why does Mc want to kill ml? I didn't understand that part. Could someone explain this to ...

If i remember right, the dude that raped him at the start told him the only way to get his knight’s pride back after killing the old emperor is to kill the new king, cuz it’ll make the old empress happy

I think there was also an element of "do it for the queen, she's gonna be in danger if you don't kill him" cuz she had been kind to him in the past