Haida would have chosen inui because ever since retsuko was not nice to him mostly but super rare for retsuko to be nice to him, inui was very sweet and gentle, caring about haida a lot and was never mean to him.
Theory about season 4[]
Season 4 is most likely about and haida and inui getting together and haida noticed that he made a mistake and apologizes to inui that he choose wrong and inui accepts it then haida chooses inui then haida and inui are now together also retsuko let haida choose inui.