I think that was the main plot twist and a lesson also you could say that your perception and affection for people does not guarantee that they will reciprocate it in the same manner. Natsumi could well have almost not acted on her feelings at all for her regard for her Haru if she hadn't stumbled upon those posts and I'm so glad she did because atleast she got to know the truth, no matter how much it may have hurt and she could make the decision that would bring her happiness.
Haru No Noroi