Man, If what you said is true then to me, this manga is awesome and it indeed has a good ending (of course not to the characters, but to us reader).
Actually, I rage quit this manga long ago because I thought: "Nah, just another pointless story where the idiot sacrificed all he has to love and save the stupid, unfaithful bitch. I bet it would just like every other times, he will somehow magically save her, they accept each other and live happily ever after". But look like your post prove that I was wrong. In one way or another, justice was delivered. The bitch shown her true rotten self clearly to the point that no can argue "She wasn't wrong, she was just too selfless, she just thought about others before herself...blah...blah" and she was literally brainwash into some kind of mindless living doll. A proper end for someone who can't even make a decision for own her life. And for the main character, it seem he will have to face the hollow shell of his former lover for the rest of his life. Everyday, she will remind him of how she used to be, how much he used to love her and how much she isn't worth it, as if that's a punishment for being too ignorant and falling in love with someone who isn't deserved.
Geez, only if an ending like this happened in Kimi no Iru Machi and Chisa x Pon