What I do agree is that his attachment to Mokhwa was a bit too fast. While liking him is alright, full on crying and killing for him seems a bit out of character even for Nakwon. He fell really hard and that can happen to some especially people like Nakwon who lead a boring like and then get fixated on that one thing but still. It was a bit too fast.
So like my point is. Nakwon is not a sociopath nor a psychopath. Just a dude with a boring like who needs some spice in it otherwise he doesn't care about anything.