He would probably try to figure out what went wrong. Harry is a curious and determined character. He might start to recall recent events to see if there were any signs of his friends' discontent. He could also try to reach out to them, either directly or through mutual acquaintances, to ask for an explanation.
Harry can focus on self - improvement. He can pour his energy into his studies, become an expert in different branches of magic. This would not only boost his confidence but also make him more independent. For instance, if he masters advanced potions making, he'll feel a sense of accomplishment on his own.
At first, Harry would be in disbelief. He would think it was some sort of joke or misunderstanding. But as the reality sets in, he would become a bit of a loner. He'd still have his sense of right and wrong, so he might continue to fight against the dark forces on his own, all the while hoping that his friends would come to their senses and realize they made a huge mistake in betraying him.
He might turn to his studies more intensively. Since he has no friends to distract him, he could pour all his energy into learning new spells and magic, becoming more powerful in the process.
He might initially be confused. Harry could keep trying to engage with his friends as usual, not really understanding why they are being cold towards him.
He might be very sad at first. Harry has always valued his friends, so being forgotten by them would be a huge blow.
Hermione would probably be very cautious at first. She would be worried about the potential danger that Tom Riddle could pose, even as a child. But she might also see it as an opportunity to study the roots of dark magic and how to prevent someone from turning to the dark side.
Well, at first, most of Harry's Gryffindor friends would be taken aback. They have always had a certain animosity towards Slytherin. But as time goes on, if they see that the Slytherin Harry is betrothed to is kind - hearted and doesn't hold the same prejudices as some of the other Slytherins, they might start to come around. For instance, Seamus might start to joke around with the Slytherin, and Dean could start to include them in group activities. It would be a slow process of acceptance as they get to know the Slytherin better through Harry.
One possible reason could be jealousy. Maybe Harry has achieved something great and his friends can't handle his success. For example, if he gets a very important role in a magical competition, his friends might feel overshadowed. Another reason could be a misunderstanding. Harry might be wrongly accused of something, like being in league with the dark side, and his friends, in their fear or haste, abandon him without giving him a chance to explain.
One possible plotline could be Harry feeling extremely depressed at first. He might isolate himself even more, spending long hours in the library or wandering the Forbidden Forest alone. Another plotline could involve him finding new, unexpected allies who help him grow stronger and more independent. For example, he could befriend some of the house - elves who have their own unique magic and knowledge.
Well, Neville and Luna would have unique reactions. Luna would likely see it as a beautiful and magical event, perhaps even having some far - out theories about the baby's future abilities. Neville, being the kind - hearted person he is, would offer his help with any gardening or plant - related magic that could be useful during the pregnancy. Ginny might be a bit protective of Harry at first, but then warm up to Daphne as she realizes how much they love each other. Overall, their friends' reactions would be a blend of surprise, support, and a bit of worry in some cases.