A Side character's jealousy Cheong san x reader WIP

Y/n, one of on-jos friends meets who seems to be on-jos childhood bestfriend. Cheong san. They are soon forced together to survive during a thrilling apocalyptic epidemic in the school, now spreading throughout hyosan city. A series of jealousy takes over as you watch on jo and cheong san interact as best friends (You basically replace on-jos role as cheong sans lover. though you think he belongs with on-jo.)