Harry could react in different ways depending on his own feelings towards Hermione. If he has some latent romantic feelings for her, he might be more attuned to her jealousy and try to make it up to her. He could start including her in his activities with Daphne. However, if he doesn't have those feelings, he might just see her jealousy as an annoyance and tell her to mind her own business. But overall, he'll probably be quite perplexed as he didn't expect this reaction from Hermione.
Harry might be really confused at first. He doesn't understand why Hermione is acting so strange. He might try to talk to her about it, but if Hermione is being stubborn, he could get frustrated. He could also be a bit oblivious and just think Hermione is being overprotective as a friend.
Well, Hermione could start arguing with Harry. She might say that he misread her actions or expressions. She could bring up past events to show that she has no reason to be jealous, like pointing out her own achievements and contributions which should make her above such petty feelings. And she may also question Harry's motives for saying so, wondering if he is trying to manipulate the situation or her emotions for some other reasons.
In these fanfictions, Ron's jealousy is portrayed in various ways. Sometimes he'll try to interfere with Harry and Hermione's time together. He might create small misunderstandings between them on purpose. Other times, he'll show his jealousy more subtly, like by looking sad or disappointed when they share a private joke or moment. His body language can also give it away, like crossing his arms and frowning when they are being friendly with each other.
The jealousy in this fanfiction scenario can have a complex impact on their friendship. Hermione's pride in her academic achievements is a big part of her character. When Harry gets good grades, she might feel like she's losing her 'edge'. This could make her distance herself from Harry. But as the story progresses, they'll realize that they each have their own strengths and weaknesses. Harry's success in grades doesn't diminish Hermione's intelligence, and they'll learn to support each other again, strengthening their friendship in the long run.
Often, Ginny will try to insert herself between Harry and Hermione. She might constantly try to get Harry's attention when he's with Hermione or try to exclude Hermione from activities that involve Harry. In some fanfictions, Ginny might even spread rumors about Hermione to try and drive a wedge between her and Harry.
A favorite scene in such fanfiction could be when Hermione finally confronts Harry about his actions that made her jealous. There's a lot of tension in the air as she tries to hold back her emotions but fails. Harry is left stunned and realizes how much he means to Hermione.
He might be confused at first. Harry isn't always the quickest to understand Hermione's motives right away. So he could just stand there, looking at her with a puzzled expression on his face, not really knowing what he did wrong.
Friendship is a very common theme. Writers often explore how Harry, Hermione, and Daphne can form a strong bond despite their different backgrounds. For example, Harry being the Boy Who Lived, Hermione the Muggle - born genius, and Daphne from a different pure - blood family.
Harry could initially be in shock. He's always counted on Hermione, so her abandonment would be a huge blow. He might feel a sense of betrayal and confusion.
It could be that Hermione feels overshadowed in general. Harry is already famous in the wizarding world, and now if he's also doing well academically, she might worry that she's becoming less important. Also, she might be afraid that Harry is getting all the attention from the teachers, especially those she really respects, like Professor McGonagall.
Perhaps she tries to find them right away. Using her intelligence and resourcefulness, she starts to search for any clues as to where they might have gone. She could ask other friends, like Neville or Luna, if they have seen Harry and Ron. And she might be determined to bring them back, not willing to give up on their friendship easily.