I do get suspicious of some parts ang have some thoeries:
1. The two chracters could actually be just a one person, meaning a person with polar disorder and could only be hallucination.
2. Ho hyun, could be a more crazier person than that sunbae and hu could have just a temporary amnesia.
3. It's just me overthinking and overanalyzing the situations, but you don't know, it could be, maybe.
Dead man Switch