I always wondered what Kaeori ment at the end about messing up the relationship with Sumi's brother. Did she mean she messed up the relationship? Like it was her fault fault that her husband turned out to be a cheating dick. Or did she mean she messed up by falling for the jackass to begin with?
She meant the divorce, but she realised that it was a necessary ''mess up'', it was justified since he was a cheater and also it led her to meeting Sumi. A lot of people stay married regardless of cheating just because they want to keep the appearance of a 'perfect life/family/relationship' or to not cause an uproar. I'm glad Kaori didn't put up with it!