And let's not pretend that 90% of the blame isn't on Yuni. If she was unsatisfied with their relationship, she should just COMMUNICATE it instead of cheating. There's nothing specail about any of this cheap drama. "Girlfriend with a victim complex doesn't communicate about her disatisfation with her girlfriend, cheats on her and refuses to take any accountability." It's just that simple... Nothing complex to it. Dunno why some people are making this unidimensional story more than it actually is...
Yuni was the one who chose to cheat and she should've been more open with her frustrations, but you can't deny that Nanase has been a pretty terrible girlfriend. It's not just being so focused on volleyball, the real problem is that Nanase is terrified of any display of affection that could possibly reveal their relationship. She won't hold hands, she won't let Yuni upload pictures of the two of them, and this all demonstrates that Nanase is unwilling to put as much passion into their relationship as Yuni is. And Yuni did tell her this at the festival, Nanase promised to do better and then went back to her old ways. Nanase missed their anniversary, apologized, promised to do better and then went back to her old ways.
Yuni didn't decide to just go and cheat out of the blue. She cheated because Fuuko exploited the emotional gap between them, offering her everything that Nanase refused to provide. Was Nanase planning on hiding their relationship forever?