I feel like most of the people in this comment section either skimmed through the manga or just skipped straight to the latest chapter.
Yes, they have sex. Yuni thinks about three distinct times they did it, literally in chapter 2.
You're talking about page 20, right? when Fuuko asks Yuni about sex with Nanase, and Yuni pictures herself and Nanase having sex during 3 panels.
I always thought it was a fantasy. Like Yuni went "Eh? Me and Nanase, have sex?" and then imagined for a few seconds what it would be like. But let's assume I'm wrong and it was a memory.
It doesn't look at all like she's thinking about three distinct times; more like it's a sequence of 3 scenes of the same roll in the hay. And it's certainly a memory from a while ago (since Yuni has been frustrated for some time when the manga starts) and we know for a fact that in the following 4 or 5 months nothing at all happens between Yuni and Nanase. So even if that part in page 20 was a memory and not a fantasy, it means they've had sex once (prolly when they became a couple) and then zilch for half a year. The case about Nanase having no real interest in Yuni's body still stands strong.
You guys should probably catch up with the missing chapters 10 to 15 on mangadex, because i really feel like most people here are talking without having read the entire manga lmao
Chapters 10 to 15 are clearly a big development arc in the manga. It starts with Yuni and Fuuko bonking at the Osaka hotel (btw a sex encounter totally initiated by Yuni). Then the story goes through many important moments between different characters (my favorite is when Yuni starts crying in Fuuko's arms, complaining about Nanase, and finishes with the words "I hate that bitch...") and it all leads to the final scene in chapter 15, the climactic stairs scene. In this scene Fuuko for the first time plays hardball with Yuni and talks about stopping their affair; Yuni panics and realizes she has come to need Fuuko so much she can't stand the idea of not having her; and then, as Yuni kisses Fuuko, Nanase discovers them.
I agree these are very important chapters both for the plot and the characters' development. But I'm not sure if any of this adds any data to the matter of Nanase's interest in sex with Yuni?