they won't be. the author explains it at the end of chapter 25.
"I often get asked what the nature of their relationship is...
The woman can not know the world with her eyes; her world is made up of
tactile sensations, hearing, and taste. Because of that, her sense of distance and intimacy is probably different from others.
For him, he needs to look constantly at the purity of his attitude, his
shamelessness, his lack of restraint... All of this makes it so the temperature of their relation doesn't really fit in the category of friendship, or love.
To be precise, it's like an extremely fine veil was raised between the two, so fine
that they can't see it, but it tickles them."
essentially they share a relationship that is unlabeled, unfitting of friends and lovers.
no it’s a relationship that goes beyond labels
Throughout the story, are they finally lovers?