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.
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.
The neighbor situation could make their relationship more open. They would have more opportunities to see each other without the hustle and bustle of Hogwarts. This could lead to them sharing more personal stories. For instance, Harry could tell Hermione more about his early years with the Dursleys, and Hermione could share her experiences growing up as a Muggle - born witch. This sharing of personal histories would likely strengthen their bond.
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.
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.
Their relationship would shift from a purely platonic friendship to a deeply committed partnership. Harry would become more protective of Hermione, not just as a friend but as the mother of his child. Hermione would see Harry in a new light, as a co - parent and a life - long partner. They would have to communicate on a different level, sharing not only their thoughts about the baby but also their hopes and fears for their future as a family. There would also be some awkward moments as they adjust to this new dynamic, especially in front of their old friends who are used to seeing them as just friends.
In the fanfic, it might be due to some sort of magic gone wrong. There could be a spell that made her act out of character. It's not unheard of in the wizarding world for spells to have unexpected effects on a person's behavior and relationships.
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.
The relationship between them can be a journey. Initially, there could be some envy or misunderstanding due to the house differences. Maybe Harry envies the academic resources Hermione has in her house, or Hermione doesn't understand some of the Gryffindor bravado. But as they interact more, they learn to appreciate each other's strengths. Harry might admire Hermione's ability to think outside the box of Gryffindor norms, and Hermione could come to respect Harry's leadership skills that are so characteristic of Gryffindor. This new - found respect and admiration transform their relationship into a more profound and unique friendship.