From the pov of manga ethics, Nanao has wronged Asumi real bad by not telling Asumi her feelings.
This is something I have seen in a zillion mangas. It's always an important plot point. Eg in the After School series (that I have been rereading because a new chapter just came out) Shiine and Ichika are "kiss friends" who meet every day after school to kiss and kiss; but Shiine is secretly in love with Ichika and doesn't tell her. When she finally admits it, she bows and apologizes a hundred times, calls herself a wretch and a scumbag, says she knows she has betrayed Ichika's trust by kissing her while hiding her real feelings, runs away crying and vows never to appear in front of Ichika again. Then Ichika must go looking for her to tell Shiine she loves her too, happy end.
I'm bringing this up because it seems a lot of posters here don't realize something that for Japanese readers is pretty obvious: that Nanao is kinda playing the role of the bad guy rn as she's tricking Asumi and wronging her (again, from a manga pov) by telling her she just wants friendly sex when in reality she wants much more.