Glad to see they finally haven't done all of this for nothing, I was afraid he would flee once again.
They did bad things, sure, but in the end they made their choice. That's life, you'd better go for the relationship you are feeling that the one which is just forced actually.
We'll never know who Kaori really was actually. Maybe she was a really nice girl, maybe she was more of a bitch trying to force him to settle with her. We know nothing much of her.
I hate the sister though, even if I understand she wanted to avoid her brother leaving Kaori, it's not her who have to make this choice, leave him make it himself. Koari and his familly were too forceful to him, he actually had some courage to go against it.
Will they be a nice couple all their life ? Who knows, they are humans, and all couples don't last forever.
I hope the dumped boyfriend will meet someone else. He was plain but seemed a nice guy, respecting her. We actually saw more of him than about Kaori.