I have just re-read chapters 16 and 17
I can sympathize with Koto's feelings of fear and anxiety of losing Aya . But I gotta admit I felt icky with them living together. Aya's literally a minor/a child.
No matter what they do and no matter how hard she forces in the idea that she wants to make it work, Koto has to TRULY accept that time has already changed them both. The difference is that Aya, understandably, seems to want to risk it living her life NOW with koto in the background and not beside Koto.
Erika, funnily to me at least, is the mother both Aya and Koto now need. Regardless of her ulterior (I mean, she has the feels for Koto), she's the current anchor for the other two. Otherwise, Koto and Aya would dissolve to madness if Erika didn't throw them any lifeline.
Oh, and Erika, shoot your shot. In my experience, I'd still rather that I get rejected than not have confessed at all.
ALSO--
"The author, Kabocha-sensei, has been ill and will be taking a long hiatus. We are very sorry for the fans who have been waiting for the rest of the story, but please watch over Aya, Koto, and Erika as she recovers."
OMG, get well soon Kabocha-sensei!
