Im just gonna tell you what happened in both games.
In the main game, Naoto confess about his cuckold fetish and asks her to engage in NTR play with Kaede'a childhood friend. Kaede is very against it but concedes because this is the only cure for Naoto to have an erection.
The NTR acts escalates but Naoto is not satisfied, Kaede resisted her lust and refused to have penetration sex with the childhood friend, and he leaves the village. Now, Naoto wants Shimoyama to have her.
Naoto himself goes after Shimoyama and asks him to do the NTR plays with Kaede. Shimoyama is honestly surprised (he initially thought Naoto wanted revenge) but of course very elated to comply to his request.
It was even harder to convince Kaede this time, but she concedes again, saying that she would only let Shimoyama touch her body and nothing else.
In the last day of the NTR play, Kaede dont return home, Naoto goes to Shimoyama house and finds it empty. There is clear signs of sex in the room and he finds recordings of the NTR play in Shimoyama's computer.
Naoto discovers that Kaede lied to him in her daily reports of what she did with Shimoyama, and she had already agreed that she would have sex with him in the last day. That is also Naoto's fault, because she heard Naoto admit to Shimoyama that he wanted to see Shimoyama breaking Kaede's resistance to have sex with him.
In the recording he discovers that they went to the Inn, he goes after them and manages to listen to them having sex trough the windows of their room.
This might be where you think the "orchastrated attack" happened, one of the villagers was there watching Shimoyama fucking her and i guess she sucked his dick or something(Shimoyama made it clear that he could not fuck Kaede), Shimoyama goes to the bathroom and the villagers begs Kaede to let him fuck her, she refuses and he threatens to tell Naoto about everything he saw. Shimoyama comes to the rescue and tells him to leave and if he tries anything he will tell his wife (who he already stole) to leave him. After this Shimoyama and Kaede have sex again and she eventually let him fuck her raw and cum inside her.
The thing is, there was no orchastration. Shimoyama did not tell the villager to do that and he was not deceiving Kaede in that scene. It is true that it helped to make Kaede less resistent to the point of letting him do her raw. But Kaede was not deceived and she did not believe in any moment that Shimoyama was not a scumbag.
After all the sex, Naoto enters the room after Shimoyama goes to the shower and jumps Kaede in lust.
In the main game, Naoto asks Kaede to marry Shimoyama going even deeper on the NTR play, until Kaede ends up living together with Shimoyama and having his child.
In the new game, after Naoto jumped Kaede at the inn, Kaede decides to stop doing the NTR play, because she knows she would fall to her lust.
She starts teasing Naoto about the NTR so that he can still get an erection with her, and they stay that way for a while.
Eventually, Naoto gets unsatisfied again and pretty much brings up NTR play every chance he gets.
Shimoyama comes to the village with Aya and declares that he will steal Kaede.
After days of watching Kaede masturbating alone in their bathroom, Naoto discovers that Kaede, while still resisting Shimoyama advances, is at the edge, to the point that she even went to Shimoyama's house to listen to him fucking Aya.
After this reveal, Shimoyama offers for a couple swap, and Naoto agrees. Kaede manages to resist her lust and refuses to have sex with Shimoyama again. Kaede asks Naoto if he agreed because he wanted to have Aya, and Naoto explains that its not because of Aya, but because he wanted to see Kaede with Shimoyama again.
Then the Inn plotline happens, where Kaede will have to service the guests to help the village. They all know this is Shimoyama's plan to steal Kaede, but they do nothing to stop it.
Eventually the plan works, the sex acts keep escalating until Kaede fall for her lust and when Shimoyama ambush her when she is at her limit, she gives in and has sex with him for hours and hours until the morning of the next day.
When Naoto returns to their house, Kaede admits that she cant resist Shimoyama anymore. They go to work and Shimoyama kiss, gropes and flirt with her in front of Naoto and she just let him. After work Shimoyama calls her and she announces to Naoto that she will spend the night with Shimoyama.
When Naoto returns home, Aya is there and explains that she wants to be with Naoto again, that it was her idea to suggest the couple swap. (She is still fallen in lust and problably would have a NTR relationship with Naoto if he accepted her). She tells him that he is going to lose Kaede for good eventually, that Shimoyama really wants her and will eventually leave the village with her.
Naoto goes after them and listen to then talking. Shimoyama tells Kaede about leaving the village with him, she refuses to do it so Shimoyama tells her that instead she will let him have raw sex with him again and cum inside, she lets him do it.
The next day, Kaede does not appear at work, Naoto finds them at the beach.
Shimoyama and Kaede are talking and getting along, Shimoyama tells her that he wants her because she reminds him of his first love. While telling her the story of how he was brutally rejected by his first love, he manages to make Kaede laugh and smile at him, after flirting, he makes her admit that she likes him a little. She makes her decision and admits that she will keep having sex with Shimoyama even if Naoto changes his mind.
After having sex at the beach, Kaede goes home and Shimoyama calls Naoto out and say he know he was hiding and listening. Shimoyama tells Naoto that eventually Kaede will fall in love with him and they will leave the village together. He gives the offer to Naoto that he will not make her leave him if he convinces her to marry him.
Naoto realizes that now its truly too late to go back and he will lose Kaede for good.
He goes home and speaks with Kaede, he tells her that its his fault, he created this situation and now Kaede even developed feelings for Shimoyama, he asks Kaede to marry Shimoyama, that he at least wants to stay close to her. Kaede agrees.