It would likely cause a great deal of strain. Harry would probably feel betrayed and angry at Hermione. Their friendship, which was once strong, would be severely damaged.
They could become even closer friends. After going through the war together, they have a deep bond. Maybe they start to rely on each other more than ever, sharing every little detail of their lives.
If Hermione was Harry's sister, the relationship between her and Harry would be more family - oriented. Ron might initially be a bit jealous as he has to share his two best friends in a different way. But overall, they could form a really strong trio with a new family - like bond.
They would become more reliant on each other. Their relationship would shift from just being friends to co - parents. There would be a deeper level of intimacy and shared responsibility.
Their relationship could become deeper. Meeting Hermione's relatives would mean Harry is getting more involved in her personal life, which might make them closer. They would share more experiences related to her family, and this could lead to more understanding and trust between them.
It could show how a love potion disrupts their normal, platonic relationship. For example, if Hermione is under the influence of a love potion, she might act in ways that are out of character, like being overly clingy to Harry. This would make Harry question their relationship and his own feelings.
At the Yule Ball, the beautiful setting and the music could create a very intimate environment for Harry and Hermione. They may start to realize that they have feelings for each other that go beyond friendship. For example, they might find themselves getting jealous when the other dances with someone else. This jealousy could lead to them confessing their true feelings, which would completely change their relationship from just friends to something more romantic.
In the original series, their friendship was built on a foundation of trust and common goals, like fighting Voldemort. In a married fanfic, that trust would be even deeper. They would be more involved in each other's daily lives. For instance, Hermione might be more involved in Harry's Auror work, giving him advice on how to handle certain magical cases. And Harry would be more involved in Hermione's efforts in the Ministry of Magic for the betterment of the wizarding world. Their relationship would be a blend of love, friendship, and partnership, which is different from just the friendship they had before.
Well, they'd be closer in a more family - like way. In the original, they're good friends, but if raised together, they'd have that sibling - like bond. They'd probably be more protective of each other right from the start. For instance, Harry might not be as hesitant to ask Hermione for help as he sometimes was in the books, and Hermione would be more likely to mother - hen Harry.
In some fanfics, Hermione and Malfoy's relationship can be quite complex. Sometimes they start as rivals but gradually develop an unexpected friendship. This can be an interesting exploration of how two very different characters from the original 'Harry Potter' series can interact in new and creative ways.