The fact Nene is jealous / envious of Amane's cuteness is pretty well confirmed at this point, I think. What needs explanation is "why" she ended up feeling that way. Generally you want your romantic partner to be as cute and attractive as possible; it's not exactly normal to grow jealous of their attributes. So why and how Amane ended up feeling that way definitely calls for some explanation.
We'll have to wait and see.
I guess I’d put it that the more personal and emotionally intense Nene’s reason for the breakup (whatever it might be), the less her agreement to “stay friends” with Amane makes sense.
If, on the other hand, the breakup is motivated by romantic indifference (as she claims) or by some external factor (one of the lurking villains), then the cruelty of her responses to Amane seems disproportionate.
And, as has been pointed out, that cruelty is at odds with her apparent pleasure with and what looks very much like affection for Amane in the early photo-shoot and beach scenes. Etc.
Again, there are potential explanations for all this, but (assuming it’s not just erratic storytelling, which at this point I do not think it is) the longer it takes for us to get that understanding the more unstable and inconsistent Nene looks as a character.