C'me on, author, why draw Goto like a goofy smug bastard. He has earned this win.
He has underwent a lot of challenges and growth, while Agawa didn't!
She's the one that needed to be taught a lesson, so why does it seem to painted as Goto at the height hubris about to be hit in the back of the head.
He didn't do anything wrong, better, he's doing for once exactly what Agawa said she wanted from him. It was when he imposed his feelings on her when she was clear that she was not interested by romance, that he was in the wrong.
Now the question should only be if Agawa changed her mind, which she's allowed to do. Is she hurt after when Goto is the one that can be with everyone?
If that's the case, they need to talk and be honest with what they want. And it will be either both can be free or both will be exclusive with each other.
Not sure what she expected during the Summer break, when she didn't try to see him and instead fucked randoms after randoms, and worse kept doing it when she didn't even enjoy it. Did she want him to spend his summer alone and miserable or something?
If yes, she doesn't care about him, she only likes the attention she gets from him and he's better off enjoying his new harem with girls that are clearly into him.
The only thing in Agawa's defense might not be something new that she needs to learn from. It could be argued that it's the same old pattern that hurt her enough that it led her to only seek intimacy with guys she cared little for so that her sister didn't steal them away.
Because yes, I love her, but we can't forget that this entire arc was started by the President seeing an opportunity to snatch Goto from Agawa, when she heard he failed all his tests and she saw Agawa make the mistake to tell him she'll be fucked by whoever will he needs to forget about sex and study.
Shina completely hijacked the situation and in a way, proved herself better than Agawa by giving Goto everything he wanted without having to sacrifice anything or be cucked in the meantime. She made him the one who cucks!!
So as a reader, even if it feels great to see vindication for the protag, if I take a step back, I feel terrible for Agawa because she was once again toyed with by her older sister.
I kinda forget which is canon with the rewrite that specifically addressed their relationship, but one good thing that was lost is that the scraped chapter had Agawa confront her sister and tell her that her manipulation wasn't love and just hurting her.
But instead of having Shina put in her place and Goto refusing her, we had in the new canon Goto choosing both and have the threesome. Funnily enough, Takeda Super fell for the same horniness that Goto and put fan service before anything and pushed back some needed character resolution.
TLDR: Forget Goto, I think Agawa should slap the shit out of her sister. She played everyone like a damn fiddle!