Found a summery from sad panda
MC and his gf (Shiho) have sex for the first time after dating a year. They are childhood friends. 1 year later is when the actual story takes place. MC is getting a cuckold fetish. He likes it when guys stare at his gf. He overhears his gf and her friends talking about ever thinking of sex with another guy. Hard to understand at this part but I am assuming she reluctantly said she did. He brings it up during some sex with her and he tells her it is hot if she has fantasized about that. He tells her what if it was OK for you to try this. She thinks it over and agrees to satisfy his lust but also partly for her. She doesn't want to do it with a stranger so she suggests their other childhood friend.
So MC comes goes to his buddy with his gf and brings up the topic. It happens that the buddy also has to talk to them about something. He just broke up with his own girlfriend, but after MC drops the bombshell of asking him to have sex with his girlfriend he says he forgot. In reality he was going to confess to his friend's girlfriend and tell his friend he was sorry. He has been in love with her for a long time. That is why his last relationship doesn't last. He obviously agrees with the intent of stealing her away. This is not revealed until the last sex scene of the game.
The buddy and girlfriend go to a love hotel. It is the same love hotel and room where she lost her virginity to the MC. In the opening sex scene with MC and his gf she won't let him take a shower with him. With her bf's buddy she also refuses but he comes in anyway. He washes her and then his dick slips in. Obviously he is not wearing a condom in the shower so he fucks her bareback. You can choose where to blow his load, of course I chose inside.
After they are done fucking in the shower he fucks her in the bed. She is supervised he can have sex multiple times. Guess the MC is a one-shot kind of guy.
She is suppose to report back everything she does. She admits to the MC that it is the best sex ever. This is the part where she is clutching the pillow.
About a week later they are having sex and MC cannot get it up. He has probably been browsing on e-hentai too much and damaged his brain from all the crazy shit on here and suggests she fuck their buddy again. He says she can fuck him whenever she wants. So she calls him up and leaves to fuck him. They go back to the hotel and he fucks her once in the shower and twice on the bed. You can choose with a condom or not this time.
Later on MC while MC looks out the window of his classroom dreaming of all the crazy NTR things he can, he sees his gf walking toward the storage area while at their PE class. He then notices their buddy is also gone. Even though she was born 1 day before MC, he is in a class behind her. He fakes an illness and goes looking from her. He looks for her but can't find her. He notices a door that he is unable to open even though it has no lock on it. She was actually blowing him in that storage area and then he fucked her. She tells MC about this while giving him a titty fuck.
Later on I think he asks for a weekend with her. During this sex he confesses he loves her and for her to dump the MC. She agrees and starts to avoid the MC. She comes over with a pocket pussy and jacks him off while telling him that she is leaving him and that their buddy confessed to her. She tells him that she loves the buddy too.
MC is in denial and follows her. He sees her meet up with their buddy and the buddy tells him that he will show him to prove it. So they all go in a love hotel and the buddy ties MC to a pole in the hotel room. She and the buddy do their "routine" and fuck in the shower. They come out with her only holding that towel and kiss in front of him. He gets a boner. He takes her to the bed and fucks her.
A few months later his ex-girlfriend treats him like an acquaintance and not a close friend like before.