This is my overall opinion on the entire manga, do not read if you want to read it yourself, I will spoil basically all the most important moments.
This one made for a very interesting read. In a way, it's just like Yuuto said, they were both trash people, only enabling each other's worst habits and traits for their personal satisfaction. There was really no other way this could have ended that wouldn't also be a bad end for someone. Akira would never get together with Kai again, the possibility was never even on the table, both because she was so obssessive that he himself would never consider it, but also because Shion showed him what a happy, healthy relationship looks like. Yuuto was never gonna get a happy, fulfilling relationship with Akira because she never cared about him in any real capacity beyond how he could be useful to her, not to speak of how dependant he was, to the point he was throwing away any sense of dignity, of right or wrong just for the sake of sticking by the side of someone who couldn't give less of a shit. Even Kai, to a certain extent, showed a not so pretty side when he caved to Akira's demands and started letting her stay in his room like that, putting his relationship with Shion in jeopardy for it (Shion's a fucking angel btw). The story works quite well, with characters you don't root for, but you always wanna see just how much further they are willing to sink for the sake of relationships that were never gonna work out.
Overall, it makes for an interesting read, not necessarily a fun one, especially that moment when Yuuto finally wakes up, when he sees the "Kai room", and finally internalizes what he'd known for so long, that Akira did not and would never like him that way, it was just a disgusting co-dependant relationship. Still, the ending was at least a bit hopeful (even if she was a piece of trash, I, much like Yuuto, didn't want to see Akira end her life). Seeing them simply having a little friendly get-together, with neither acting in a trashy manner, just being good friends, did at least make me happy by the end.