That's so creepy. Where's the other dude? MC's friend at work? Is he actually dead?

He isn't dead. The author didn't mention him again after that one last scene. Probably he was transferred to somewhere else.

Lmao I love how u literally have no information, u can't prove he's not dead but u also can't prove he's alive somewhere besides the artist forget to draw him

The comment section of the raws did say Seongmin wasn't dead. But yeah, I can't prove to you that he isn't dead, but after reading S2, I don't think Seme will kill him.