Author has stated multiple times that this isn't a Yuri story. So what exactly is the plan then? Because all I can see up to chapter 14 is three (yes three) girls having Yuri action. So is the guy actually going to do something when he finds out? Is he going to find out at all? Like where is this supposed to go?
He's lying. Literally everything about the last two chapters is pointing towards this turning into Yuri. It was already mostly lesbian smut but the pretext was "training" a girl good enough for her brother since the little sister can't fulfill that role.
Then we add the guy being premature and not having sex because of it and his girlfriend thinking about the little sister as she's climaxing from oral sex, and the reveal that the little sister was depressed while Yuuka was gone and it's undeniable.
I wouldn't say he was lying. Some people in Japan have a really weird and narrow idea of what counts as yuri or not. Some authors are even on record saying their extrmely gay story isn't really yuri.
Few of my thoughts - there will be no love between girls, just pure lesbo sex - and author believes this isn't yuri, cause maybe in his mind yuri is a love/romance not just sex friends.
Another thing is what I already was theorycrafting in previous chapters - that this "fake yuri" will be the drama part. Like the sister is a bro-con, she wants to fuck him but cants, so she decided to train the girl her brother loves, so that she will be good in bed and thus make him happy. Just a small issue happening with it - bro being bad at sex/in bed, premature and stuff, while the girl is already over-trained and "needs enough stimulation" - ala NTR porn mangas where dude with huge shlong steal the girl from small dicked beta MC - cause girl finds out that he doesn't give her pleasure any more with his small PP, cause its not going deep enough and stuff (one of those made me laugh cause the NTRdude made the girl bleed and "lose virginity" again, cause the beta MC dick was so small it didn't "properly deflower her").
Aka sister trains the girl, the girl has now to high of requirement/expectations, bad at sex dude isn't able to make her reach what the sister does in the training and/or thinks about training when she goons with MC either which fucks their relationship, and thus instead of helping MC sister fucks their relationship instead. Question is - will this lead to some 3some with sister full blown orgies incest story, or will it go drama "NTR" way where the MC and girls relationship is fucked by the sister and some fighting will ensue. Or will sister learn about how she fucked up fast enough to somehow start training the brother via the girl to fix their weak sex so that the girlie could be happy with him?
I also wonder if there will be drama just about cheating. I mean girl basically has lesbo sex with the sister - its already full blown cheating. People now spoiler that
there will be female only orgies with additional new characters. Which would be even more cheating? Will bro find out? How will he react? There is no drama tag, but the psychological tag in my eyes could mean basically mental drama of sorts.