Why didn't she say that? However, if women cheat on their husband, it was thought that it was not their intention.
Every thing seems fine and dandy, suddenly a challenger appears, Boy B.
For most people it's the monster below the bed, the shadow on the wall, the fear of an unknown enemy that they know is bad.
Yuma senses though that there might be trouble between her and Fujiwara despite Hotaru's strong attitude.
An important part of Netorare is also the heart.
I like the cliché, but it is irritating to see that the protagonist ignores the feelings of the heroines and has no punishment for that.