I Need to Raise My Sister Properly

When I regained consciousness after a car accident, I became the stepsister of the villainess in "My Beloved Santa." Having already possessed this body, I decided to prevent the villainess from becoming a dark person. I worked hard with all my heart and all my strength... Somehow, I got entangled with the duke of Lexerville, who was infamous for being a bloodthirsty madman. "Didn't I warn you back then that I wouldn't let you go if you did something stupid?" When he saw me with another man, he interrogated me as if he had caught a cheating girlfriend. I asked "Do you like me by any chance?" He replied, "Stop talking nonsense." If so, why is he acting like this? (Source: Kakao Entertainment Corp., translated)