I also don't get the criticism that these chapters are straying too far from the premise. Why is it a bad thing that Asumi found someone she wants to do it with without paying for it? Was she supposed to limit herself to buying sex for the whole series? And both her and Nanao's experience with paid-for sex gave them a bit of extra courage to cross the line with each other, so the development is not random at all. I for one can't wait to see where it all goes, regardless of which ship (if any) sails in the end.
I am just way more interested in her finding Mai. That is why I continued reading. Lewd prostitution adventures, cute interactions and finally the confrontation with her childhood friend. I do not think this new direction is bad, just not something I really wanted out of this manga. If I want a manga about an adorable couple I read that one, not one about Lesbian Brothels.