One possible reason could be a misunderstanding. Maybe Harry misinterprets Draco's actions or words in a way that makes him do something that breaks Draco's heart. For example, if Draco is secretly trying to help Harry but Harry thinks he has some malicious intent and publicly shames him.
Perhaps it's a matter of unrequited love. If Draco has developed feelings for Harry but Harry is completely oblivious to it and starts dating someone else like Ginny, it would be a huge blow to Draco and break his heart.
Draco might become withdrawn. He could isolate himself from his friends and spend more time alone in the Slytherin common room, brooding over what Harry has done to him.
One reason could be love. Draco might have fallen deeply in love with Harry and his possessiveness is a way of showing his strong feelings. He doesn't want to lose Harry to anyone else.
One reason could be to add drama and conflict to the story. Fanfiction writers often like to create complex situations to make the plot more interesting. Another reason might be to explore different aspects of the characters' personalities in a non - traditional way.
In fanfiction, their kiss might be a way to break free from the expectations placed on them. Harry is always seen as the hero and Draco as the villain's sidekick. By kissing, they are defying those roles and expectations. It could also be a way to gain power over each other in a different sense. Instead of the usual power struggle based on magic or family name, the kiss becomes a new form of power dynamic between them.
In the 'harry rejects draco fanfiction', it could be due to the social divide between Gryffindor and Slytherin. Harry, as a Gryffindor, has been taught to distrust Slytherins. Draco's actions towards Harry's friends, like Hermione who is a Muggle - born, also contribute. Harry may reject Draco because he stands for the discrimination that Hermione has faced from Draco and his family.
A possible reason could be that Harry is feeling the weight of his responsibilities. He has to constantly fight against Voldemort and protect the wizarding world. When Draco sees Harry cry because of this, it shows the toll it's taking on Harry. Another reason might be a personal loss. If Harry loses a friend or a mentor, Draco could witness his grief.
One possible reason could be a newfound understanding between them. Maybe they've both grown and realized that their past enmity was pointless. They might have had some shared experiences that made Harry see Draco in a different light, and thus he was willing to accept his hand as a sign of peace or new friendship.
Maybe Draco says some really mean and hurtful words to Harry. For example, he might make fun of Harry's family situation, like his parents' death or his relationship with the Dursleys. Words like that can be really cutting and could easily make Harry cry.
Perhaps Draco has developed some sort of complex feelings towards Harry. He could be secretly attracted to Harry and treating him like a baby is a way to get closer to him without admitting his true feelings. Or it could be that Draco has changed as a person and now views Harry as someone who needs his support and guidance, just like one would for a baby.
Perhaps Draco has developed a sense of respect for Harry over time. He might have seen Harry's courage and determination up close and decided that Harry is worthy of his help. Throwing the wand could be his way of showing that he acknowledges Harry's importance in the fight against the common enemy.