It's more of an example of how his BPD is being manifested, ie having such an intense relationship, and being content with just being validated, in his eyes by Sangwoo. Sangwoo is emotionally dependent on Bum at this stage, it's codependency, and both sides are approaching their relationship in a rather unhealthy way, but at the end of the day, they feel they need each other. I find it a bit hard how people in the comments can have such a polarized view of the characters, Killing Stalking is just an example of two mentally unwell men, their back stories and how this manifests into their codependent and criminal behaviour as adults. Both men are criminals, both men have killed. Infantalising Yoon Bum is very very odd, but seems to be a popular theme in the comments. Oh well.
Am I the only one who gets sick when Bum acts as if they're some kind of newly weds? Fucking disgusting, how he blushes and all. Ew.