Even serial killers do the washing up and buy bread.
It's almost as though people forget that Bum killed two people, and one of those cases he stabbed the victim 20 times. That isn't self defence, that was to try and impress the man he was stalking for 5? years. The author is great because we just don't know how the plot will end. The police are incompetent, and the sacked detective is becoming obsessed so maybe he will try some vigilante justice. Sangwoo seems a pretty depressed and frightened person, so I would maybe think that after they feel they will be separated, as maybe after months after the murders the police cotton on to them, or the sacked detective is upping his game, they have a double suicide or him asking Bum to kill him, or Bum, after learning about Sangwoo's childhood kills him as a "mercy death" then commits suicide himself. IDK
Bum didn't kill to impress Sangwoo, if you think that you should re-read the comic with more attention. He was forced in both cases and when he killed Jieun (he stabbed her 12 times, not 20), Bum was deeply dissociating. It seems that it's you who forgot how it went. Bum is not innocent but he ended up a killer because of Sangwoo. He wouldn't have killed Jieun if she wouldn't have unknowngly triggered one of his worst memories, it's not Jieun's fault obviously but Bum is severaly mentally ill and his brain reacted like that. It's also inaccurate that he was stalking him for 5 years, it's more 3 years and he probably started stalking him after the military, so it's even less. This of course doesn't justify the stalking but you shouldn't spread inaccurate information. I agree with you on the unpredictability of the story though
I feel so uneasy reading the last few chapters. Everything is going normal, almost as if both sangwoo and bum were living a normal life together.