Draco might become withdrawn.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.
He may also try to get revenge. Draco has a prideful nature. So, he might plot against Harry, not in a very evil way but more like trying to make Harry feel the same pain he's feeling. For instance, he could try to make Harry lose his position as Quidditch captain.
Another reaction could be that Draco tries to hide his pain. He doesn't want others to see his vulnerability, especially his Slytherin peers. So, he puts on a tough exterior but on the inside, he's really heartbroken and confused about his feelings towards Harry.
At first, Draco might be in shock. He didn't expect Harry to break up with him at such a crucial time. Then he could try to reason with Harry, begging him to stay for the sake of their unborn child. When Harry refuses, Draco could turn to his own family for support and close himself off from the outside world for a while.
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.
Harry might be confused at first. He doesn't understand why Draco would think he's a doll fan. So he might just shrug it off and not pay much attention, thinking Draco is just being his usual difficult self.
Draco would probably be extremely angry. He might feel a deep sense of hurt and betrayal, especially if he considered Harry a friend or at least an acquaintance he could trust. He could start plotting revenge against Harry, using his own cunning and Slytherin skills to make Harry's life difficult at Hogwarts.
Harry's reaction would be complex. He has been at odds with Draco for so long that this revelation completely changes the dynamic. He would likely experience a sense of disbelief that such a thing could be happening to Draco. As he processes it, he would start to feel empathy towards Draco. Harry might approach Draco cautiously at first, not sure how Draco would respond to his newfound knowledge. But he would be determined to help in some way, whether it's by using his influence in the wizarding world or just being there for Draco as a friend. This could also lead to a significant shift in the relationship between the Gryffindors and Slytherins as a whole, as Harry's actions towards Draco could inspire others to look at Slytherins in a different way, seeing that they too can be victims of difficult situations.
Betrayal is a very common theme. Draco might betray Harry's trust, like revealing a secret or choosing a side against Harry, which breaks his heart.
There's also 'Fractured Bonds'. In this fanfiction, Draco breaks Harry's heart by siding with the wrong crowd at a crucial moment. It could be that Draco is pressured into doing so, but the result is Harry feeling betrayed and his heartbroken. This often leads to a downward spiral for Harry as he tries to come to terms with what has happened.
He could also react with suspicion. Draco might think that Harry has some ulterior motive, especially if the confession is of a more positive nature like friendship or love. He would question Harry's sincerity and might even test him in some way.
She might be heartbroken at first. Hermione is someone who invests deeply in her relationships. She would likely retreat into her studies as a way to cope, burying herself in books to try and forget the pain.
Harry might initially be very angry and hurt. He could cut off all communication with Draco and become withdrawn. In some fanfics, he would even start to avoid places where he might run into Draco.