He's not actually a ghost because he's still alive. It seems that he has been having a lot of problems in life so at night his bed and his body becomes,visible in the veranda of the dark haired guys home for unknown reasons. The dark haired guy can see what he is doing but the guy with the light doesn't know about it. By the end of the chapter we are told that he doesn't have any regrets anymore so the dark haired guy is not able to see the what the light haired guy is doing anymore.
Or the reason he's not able to see him on veranda because they have sex everyday lol
Author explains in the story that he could be a living spirit via MC's convo with his coworker. It's a phenomenon that has a history in Japanese lit (see Tale of Genji, Lady Rokujo) Basically, a person who harbors strong desires/negative feelings unwittingly allows their spirit to wander. The spirit stopped wandering because MC's new relationship with him filled in his emotional void. Kind of different in this instance though, since MC seems to be looking into the guy's room in real time, so it's more like tuning into a radio channel or smth rather than meeting a spirit, but it still kinda makes sense to me ¯_(ツ)_/¯
Ok so what??
Was he a ghost? People can see him... wtf I'm confused