From this chapter it feels like the point of the story is starting to come across. Yuni being a teenager has a shallow perception on how love works, thinking that there can only be one person in her entire life that she can love, so instead of communicating or/and breaking up with her, she just follows her heart to the fuuko whom she loves more. But she doesn't want to admit that she isn't getting what she expected from her relationship with nanase because she still likes her as a person, but she's confusing romantic love with platonic love and this chapter shows it, not to mention feeling indebted for the pain she caused.
It's easy to have these conflicting emotions as a teenager who's still trying to discover their identity and understanding of everyone else. Especially if they're attracted to the same sex.
Obviously they're not supposed to be likeable, but I think this is a story worth telling, in my opinion, what the story is trying to tell is to communicate with your significant other instead of doing extremely painful things like cheating. If it doesn't work out, break up with them, and it'll hurt much less than cheating.