I’m surprised by the low rating. But after reading some of the comments it looks like it’s getting lower ratings cause some don’t seem to understand the purpose of this type of story and just have the black and white view of “any cheating = wrong/horrible”.
Is extramarital affairs “wrong”? Well, depends on how both parties are behaving and the exact circumstances leading to it.
Also I don’t know what marriage laws are like in Japan. Things like divorce/separation can be very difficult to do (both economically and socially speaking). So it may not be possible?
Anyways I think people should give this story a try cause it’s not bad.