One possibility is that Harry would be extremely hurt and angry. He might immediately confront Ginny about it. He could cut off all ties with her and distance himself from their mutual friends as well, feeling betrayed not only by Ginny but also by the false image he had of their relationship.
Well, Harry could also try to find out the reasons behind Ginny's cheating. Maybe she was being manipulated or there were some misunderstandings. He might initially be furious but then start to investigate the situation more calmly. If it turns out there was some external factor, he could be more forgiving, although the relationship would never be the same.
One possibility is that Sirius could be initially shocked. But then, being the understanding person he is, he might give them his blessing. After all, he has seen how Harry has grown and Ginny is a great girl.
One possible outcome could be Naruto feeling extremely hurt and betrayed. He might distance himself from Sakura completely. In the context of fanfiction, he could also focus more on his training and his other friendships, like with Shikamaru or Kakashi. He might become more determined to prove himself without Sakura's support.
It could cause a scandal in the wizarding community. People might take sides, with some supporting Harry and others thinking there must be more to the story. The Weasley family's reputation could also be affected. Ginny's actions might be gossiped about in places like Hogwarts and Diagon Alley.
Perhaps Snape would force them to work together on a task as punishment. This could be something like cleaning the Potions classroom without magic or helping in the Forbidden Forest. During this time, they might start to understand each other better. Harry could see that Draco isn't just a spoiled brat all the time, and Draco could see that Harry has more depth than he initially thought.
Another scenario could be that Ginny accepts but on the condition that they go on an adventure first. They could travel around the wizarding world, visiting different magical places they've only heard about, like the hidden valleys in Romania where dragons roam, before settling down to plan their future together.
Ginny asking Harry out could lead to a very interesting chain of events. It could cause some jealousy among other students who have a crush on either of them. Ron, for example, might be a bit taken aback at first but then come around to support his sister and best friend. As for their date, it could be something unique like a midnight stroll in the Forbidden Forest (with proper precautions of course), where they talk about their fears, hopes and dreams, deepening their connection.
One possibility is that Ginny would be overjoyed. She has loved Harry for a long time. She might immediately say yes and then they would start planning their future together. They could think about where to live, perhaps near the Burrow or at Hogwarts if they both end up teaching there. Their friends would be very excited too, and there would be a big celebration at the Burrow with lots of Weasleys and their friends like Hermione and Ron all gathering to congratulate them.
When Dean walks in on Harry and Ginny in fanfiction, it could set off a chain of events. Maybe Dean tells other people about what he saw, which could lead to rumors spreading around Hogwarts. This could put pressure on Harry and Ginny's relationship. On the other hand, it could also make them stronger as they face this challenge together. They might have to deal with the disapproval of some students or even teachers who think that their relationship is inappropriate or that Harry has betrayed Dean. But in the end, they could prove that their love is real and overcome all the obstacles.
Well, Bill might be really surprised at first. If he's a big fan of the original story, he could be either intrigued or a bit put off by the fanfiction. He might start reading it out of curiosity to see how others are imagining Harry and Ginny's relationship in different scenarios.
Well, it depends on the tone of the fanfiction. If it's a more comical one, Mrs Weasley might make a big fuss. She could start ranting about how they're too young and that there are more important things to focus on. However, if it's a more serious and romantic - themed fanfic, she may just give them a knowing look and a gentle warning to be careful.