Although this is something that mangas lack, I have to admit because the story never really shows when and why each of the characters fell for each other, I cannot get attached and understand just how they've kept such strong feelings apart for the sake of the story
Emphasis mine. Some comments claim Koto is neurodivergent but I see no evidence of that.
More believable is having no answers from Aya's disappearance left her with a trauma that hampered her ability to form new connections. But seeing as Erika, who does not appear traumatized, went completely celibate in the same timespan while nursing her crush on Koto, I think the author simply hopes the reader will buy-in to the characters' affections remaining unchanged after 7 years for the sake of the story despite it feeling unrealistic.
Also, manga is the plural of manga