Bum

Some fans seem to be confused about Bum's behaviour. Let me clarify that ;) . Whenever Sangwoo isn't pleased with Bum's behaviour, which means Bum's life is in danger, Bum starts to compliment and/or seduce him. He does that since he found out about Sangwoo's real personality and Sangwoo never kills him because of that. The first time he did it was when Sangwoo found him in the basement. In chapter two he thinks "I'm going to die! I don't want to die" and then he confesses to Sangwoo, he tells him how much he likes him and that's how he survived that situation. It's also very obvious in chapter 8. In chapter 4 Bum really wants to have sex with him but only because Sangwoo treated him very nicely and that's the Sangwoo Bum imagined when he was his stalker. The way Bum acts in ch. 4 isn't the same as in ch. 16. In ch. 4 he gets excited and hard but in ch. 16 he's shaking and doesn't even want to open his mouth. We don't see Stalker-Bum in ch. 16, we see "oh, shit, I don't want to die" Bum.
Sangwoo wants an obedient slave who does whatever he's told to do and meanwhile Bum knows that (gets pretty obvious in the official translation of ch. 15). It's Bum's survival strategy. Bum has two sides, Stalker-Bum and Survival-Bum. I don't know how often we'll see them again, or if we'll ever see them again. His breakdown in ch. 15 and the way he acts in ch. 16 could mean that he's given up, maybe Sangwoo broke him completely and neither Stalker nor Survival-Bum survived and we'll only see Sangwoo's loyal slave from now on. But it's really hard to tell at this point. Sangwoo's easy to predict but Bum's character is pretty complicated.