She's talking about having hurt her best friend, isn't that normal to also have people you like outside of your girlfriend? They are partners, isn't it fine to share your personal life and your regret? Yuni complain that Nanase don't support her emotionally but she just doing the same thing here...
Exactly, Yuni is such a bad girlfriend or even human being that she can't bear the thought that someone can have a life outside of her. At best, it's imaturity and at worst, it's malevolence.
Honestly, why are they still together? Nanase is telling her girlfriend about something deeply personnal and intimate and all she can think is "man, this is so boring" and then proceed to gaslight her that she should go see Fuuko, the one she CHEATED with. How selfish can she be? Like she could...
Aside from the god being first introduced as menacing from the start, then being revealed to be kind then having another twist with them now being the villain, I find the main conflict of the story kinda strange and interesting.
Like, Hinata main goal is to not be an ogre anymore so she can love...