Killing Stalking isn't everyone's personal preference, and I think that's reasonably so. I only completed the manhwa 3 months ago, and I'm relatively new to the yaoi/webtoon community (not that Killing Stalking is a yaoi or a BL), so I can't dive into further detail about that. I personally enjoyed reading Killing Stalking for the ominous and unpredictable plotline, as I had seen the manhwa appear on a few websites listing the top mainstream BL webtoons, but as I dived into the story, I quickly realized it wasn't anything like what these websites claimed.
The characters are unfathomable and sinister, and I thought the art was drawn beautifully, as the features of the main characters were not romanticized in any way. Killing Stalking is by no means a mere love story, and yet the portrayal of their love is warped in the most awful way possible. The derailment and ruination of the characters as they spiral into insanity is absolutely heart-wrenching and torturous for the reader, so-much-so that a good majority of people have difficulty reading further, or even reading those few particularly troubling scenes, one person being myself. (I was fortunate enough to be able to make it to end, however.)
The depiction of the trauma that both Sangwoo and Bum faced (and still do face) is what intrigued me the most about this manhwa. In a perverse way, the story of Sangwoo and Bum is a re-enactment of Romeo and Juliet. Their fates are so intertwined that the words of one become the actions of another's, and that, tragically, is what twists into the demise of Sangwoo and Bum.
This manhwa gave me so much anxiety that I couldn't read a few chapters without pausing and having to evaluate each chapter before proceeding to the next. I didn't hesitate to research the ending of this manhwa, and when I did, I found that I had been even more anxious to read the next chapters than I did before. Sangwoo's death literally haunted me in my sleep, and I began to regret even reading the manhwa in the first place. (To be fair, I do have OCD and social anxiety, so it may not have been the manhwa after all. I also panicked about Sangwoo's death before actually reading the end...yikes.)
My anxiety became so terrible that I started developing a condition known as maladaptive daydreaming. According to Wikipedia, it is stated as being "known as excessive daydreaming, [and] is a disordered form of dissociative absorption associated with vivid and excessive fantasy activity that often involve elaborate and fanciful scenarios...People who suffer from maladaptive daydreaming can spend more than half their days in 'vivid alternative universes.'" (I can give you one hint as to who those "vivid alternative universes" were about...)
As being someone who is not aware of what people in the mainstream had to comment about Killing Stalking, I certainly do not "ship" Sangwoo and Bum by any means. People need to be cognizant of the difference between yaoi/BL webtoons and psychological narratives. It's unfortunate that so many people in today's generation think that because Sangwoo and Bum have kissed and engaged in sex, that they are "clearly in love" or "exploring their sexuality together." (I am fully aware that Bum did not engage into sex willingly with Sangwoo, nor is Sangwoo homosexual.)
I enjoyed the psychological aspects of the manhwa, as well as the mental disorders that are not-so-subtly portrayed, and if the author, Koogi, had spent a bit more time detailing Bum's plans of escape, or at least had made an attempt at having Bum break out of Sangwoo's clutches once or twice, I think I could take the time to fully appreciate this manhwa in its entirety.
P.S. I apologize for my extensive answer — I am hoping to become an English and philosophy major in the future, coupled with the fact that I have OCD and any grammatical errors would probably send me over the edge. (Kidding! Not really...)
Thank you so much! (づ ̄ ³ ̄)づ
Just to say I really like your answer (⌒▽⌒)