Okay let’s just put this to rest with facts or plausible theories
Yoonbum and Sangwoo both have personality disorders and dark pasts
Yoonbum and Sangwoo are not in a healthy relationship
Yoonbum and Sangwoo are both criminals
Yoonbum is scared and acting out of either dependence or a twisted Stockholm syndrome; he also had feelings prior to being held captive possibly clouding otherwise clear connections- he may be slowly viewing Sangwoo as less of a monster and more of an ally
Sangwoo is possessive and acting out of either a disconnect due to his upbringing or a prior mental instability only heightened by his parents deaths. He shows signs of a superiority complex and seems to view most below him- he views Bum as a mother figure with an Oedipus twist
I’m saying this again: Sangwoo and Yoonbum may be misunderstood but they are still criminals
Sangwoo seems competent enough to be tried against if his crimes come to light, he does not kill out of insanity and the torture and brutalization of the bodies along with collecting the clothes seem to point in the acts being based on power and possessiveness. This most likely is a replication or evolution of his fathers actions against him
Yoonbum is, ironically given the lack of severity in his crimes, the more mentally unstable, he would be pitiful in court but his previous offences may put him at a disposition if he chooses to get help once a new chance arises. He is showing signs of becoming manipulative out of necessity for survival. Most of his prior actions can be explained as symptoms of a under-treated or severe case of boarderline personality disorder.
Killing Stalking isn’t about a ‘hot sexy bdsm’ it is about psychological and physical abuse and how it develops into either reliance or rejection- basically what I’m saying is most aren’t reading this as a 50 shades of grey knock-off and are treating it as it is, a horrifyingly curious story.