Responses
Were you the one who asked this same question about a week ago?
Because I spent hours searching for it that night and couldn't find it. But I found it just now!
http://www.mangago.me/read-manga/shinonome_tantei_ibun_roku/
Omg that's it! Thank you so much!
A yaoi oneshot where a man (detective?) stumbled upon a male ghost who wears a yukata. The ghost worked in the sex industry or brothel during his lifetime. There is also an old man who was the ghost’s lover (?). The old man, when he was younger, left the ghost (who was still alive) and the ghost was devastated and eventually died.