Responses

I think he mentioned something about his naiveness and his submissive nature. He doesn't second guess Kangwoon demands he just does it. Plus Kangwoo likes power so it's like a good ego power boost to have someone who likes you but is also afraid of you. That's just my guess but I'm sure it's probably more.
I wonder, if we'll ever get an explanation for why Kangwoo is so obsessed with Heewoon. He may be an abusive and obsessive little bitch, but in his own twisted way, he clearly cares for Heewoon and so far there has been no explanation as to why.
Kangwoo clearly new, Heewoon used to stalk him all along and yet never did anything about it until he couldn't ignore it any longer (pretty sure, in the novel, he even states, he liked Heewoon stalking him and gives him permission to continue doing it lol) , so there must have been SOME positive feelings there before the start of the story.