Cheum gets painted a hero and a sunshine for trying to manipulate her friends into coming back together when she didn't even go looking for Boston to apologize to him when she found out that her brother lied about.
Mew asks if he's an asshole for not forgiving Boston and Top just gives him a big speech about how it's totally his choice who he keeps in his life because, obviously, Mew is making the right choice.
No one ever apologizes to Boston unprompted except Nick and, in fact, almost no one ever apologizes to him at all.
Because he isn't monogamous, because he's honest, because he's an asshole just like all of them, but he owns that part of himself different than they do and so they must reject him and leave him alone in the end.
Was Boston as ass at points? Yes. But so was literally everyone else.
But only Boston has to pay the price because Boston isn't monogamous and so he doesn't deserve the same happy ending everyone else gets. Because if you're not made for monogamy then you don't get to be happy. You get left alone by everyone, all your friends and all your lovers, no matter how honest and how much you try and what you say.
The crime of being non monogamous earns you no forgiveness and leave you alone.