He knows that Jinha’s only acting cold to Siwon to redirect his attention from Siwon so...he asked, “Why am I so happy?” Because next to Lu Xuan’s/Noh Seonyun’s name should be descriptives such as: schadenfreude, psychopath, jealousy/envy, homewrecker, lonely, unsavory, etc...
He knows that Jinha’s only acting cold to Siwon to redirect his attention from Siwon so...he asked, “Why am I so happy?” Because next to Lu Xuan’s/Noh Seonyun’s name should be descriptives such as: schadenfreude, psychopath, jealousy/envy, homewrecker, lonely, unsavory, etc...
We can add more~