I'm not sure why everyone here is on the Nanao train. Asumi liking sex and it being readily available with Nanao is like giving an addict her fix, but there was no indication of feelings from Asumi's side here.
There are definitely indications of feelings from Asumi's side, but she's hung up on her old crush. If she wasn't, she almost certainly would have made things official with Nanao by now, and that's why people are on the Nanao train. Embracing a healthy relationship directly in front of you is way, WAY healthier than continually dragging yourself to brothels in hopes of hunting down a rumor that a girl you once had a crush on might be one of the girls there.
Like the line, "at this point I'll go from having a friends with benefits to having a sugar mama" still implies that Nanao isn't really being seen as a partner, and more importantly Asumi isn't thinking about her feelings towards Nanao at all. Nothing has changed from chapter 16. If anything, the date chapter was at least more romantic than the context sex they're having.
Sure, but the point isn't that they are more romantically entangled, the point is that they should be, and they aren't because Asumi is so hung up on a fantasy of someone she knew years ago that she's ignoring a golden opportunity directly in front of her face. It's amusing, fairly human, leads to lots of sexy situations, and makes for a fun story, but it's definitely granite levels of stupidity on Asumi's part.
I don't disagree that Asumi has an unhealthy mindset towards Mai and finding her, but that's not what I'm talking about. I fundamentally disagree with this line:
Embracing a healthy relationship directly in front of you is way, WAY healthier than continually dragging yourself to brothels in hopes of hunting down a rumor that a girl you once had a crush on might be one of the girls there.
The implication seems to be that it's healthier because Nanao has feelings for her and their relationship isn't based on paying for sex, which sure, that is healthier. But the idea that because Nanao loves Asumi therefore Asumi should get into a relationship with Nanao, that feels toxic to me. Asumi doesn't owe Nanao feelings. And that's kind of my point, even if it is just because of an emotional hangup, that still means Asumi doesn't have feelings for Nanao. Being in a relationship with Nanao wouldn't be fair to either of them.
At the end of the day, even if Mai didn't exist, there is no indication that Asumi would choose Nanao. Of course, feelings could develop later, adults don't get into relationships with each other having equal feelings at the start necessarily, but that also means there is no guarantee that feelings will develop. They're being really intimate, and Asumi is still thinking brothels would indicate, if anything, that she has not become more emotionally vulnerable with Nanao.
To use a different manga as an example, Sorry but I'm Not Into Yuri, the main character in that is intimate with a number of different girls, but only two of them feel like she could have feelings for (one at the moment) whereas the others are purely sexual. Nanao is still in the purely sexual category for Asumi.