I think Nanjo just finds Mok-yeon cute right now. He’s the one in control, and this younger guy who used to be so arrogant and loved messing with his head has basically turned into a puppy, eagerly waiting for any bit of affection Nanjo is willing to give him.
After that huge fight, the tables have completely turned. Mok-yeon used to act like he had Nanjo wrapped around his finger, and now he’s the one trying so hard to please him. And Nanjo is loving it.