I came back to this manga since I stumbled on the mangaka's new work and from what I read of his series works, there seems to be a lot of similarities. In levels and chitose, FMC was fucked and taken by other characters while MC chickened out on confessing his feelings thus not having the chance to have sex with FMC. Both series also gave consolation to MC in a form of a blow/hand job from FMC at the end. I'm guessing the new series, You are Guilty, will also follow the same route as the past two works. Got to say, Seto Yuuki likes to cuck the MC--poor bastard.
MC is a loser, I'm glad he became NTR
FMC is a disgusting slut
Not recommended at all
I really wouldn't call both this as an NTR and the FMC as a slut since we never saw her had sex with anyone other than the gorilla boy. MC was cucked, for sure, but he still ended up with a sex friend and can still woo the kouhai. Wish there was an after story with the last chapter.