When Sangwoo says "I was getting... Worried..." In the latest chapter, do you think he really mean it? Worried about what? Worried that Bum would cut himself again? Or that Bum would escape?
I think that Sangwoo was legitimately worried for Bum’s safety in this chapter, which also explains his reasoning for bringing Bum to work (which by the way was extremely risky in his situation).
What happened in Chapter 27 was nothing short of an emotional breakdown for Sangwoo. Bum attempting to take his life opened up a plethora of repressed fears and memories, most of which he would not want to revisit. It also instilled the realization of just how much Bum means to him (for keeping his mental sanity among other reasons). Bum is not the only one mentally and emotionally recovering in this chapter, Sangwoo has a lot to work out himself before things start to be routine again.
With this being said, Sangwoo is doing everything in his power to ensure that this doesn’t happen again. Leaving Bum at home by himself would potentially open up another opportunity for him to harm himself. It’s also worth mentioning that he’s in an extremely fragile state (i.e. his wounds have not yet stopped bleeding). Therefore he was willing to put himself on the line and bring Bum to work, simply to keep an eye on him until he feel’s that Bum is well enough to be left home alone again.
So, in short, Bum being in the bathroom for too long would inevitably cause Sangwoo to grow worried for Bum’s safety.
(All panels belong to Koogi and Lezhin)