Ginny would be angry as well as sad. She has been through a lot and to have Harry leave her for Cho would be a huge blow. She might lash out at both of them. Cho would be cautious. She remembers how things ended with Harry before and would be worried about getting hurt again. Harry would be in turmoil. He knows he's hurting Ginny but he feels like he has to follow his heart towards Cho, and he'd be constantly thinking about the consequences of his actions on everyone involved.
Ginny would likely be heartbroken. She's a strong character but she loves Harry deeply. She might start to question herself and what she did wrong. Cho, on the other hand, would be surprised but also happy. She may have still had feelings for Harry all along. Harry himself would be conflicted at first, feeling guilty for leaving Ginny but also excited about the possibility with Cho.
In this type of fanfiction, it could be that Harry has some unresolved issues from his past relationship with Cho. He sees Ginny as a distraction from dealing with those. But as time goes on, he can't ignore the pull he still feels towards Cho. He may leave Ginny when he realizes that he can't move forward in his life without exploring what could have been with Cho again.
Harry might be initially in shock. He can't believe Ginny would leave him and their child. He could become withdrawn, not really knowing how to deal with this new situation.
In the fanfic, their relationship could develop gradually. Harry might be hesitant at first due to his past experiences with Cho. However, Ginny's warmth and understanding draw him in. They might start off as friends, sharing secrets and having deep conversations. As time passes, they realize their feelings are more than just friendship and start a romantic relationship. Ginny's family also plays a role, as the Weasleys welcome Harry, which makes him feel more at home and closer to Ginny.
She might also be sad and heartbroken. Ginny is a strong character, but being left alone while pregnant is a huge blow. She could withdraw from her friends and family for a while as she tries to come to terms with the situation and figure out how to raise the child on her own.
Ron would be furious. He would immediately start looking for Ginny and would probably want to confront Harry without thinking. Hermione, on the other hand, would be more rational. She would try to figure out why Harry would do such a thing and look for clues. The Weasley parents would be extremely worried and would likely reach out to all their contacts in the wizarding world for help.
Ginny herself might be conflicted. Even though she made the decision to leave, she would still have feelings for Harry. She could be sad and second - guess her decision. The Weasley family would be divided in their reactions. Molly would be worried about both Ginny and Harry, trying to patch things up. Arthur might be more understanding of Ginny's need for independence but would also hope for a reconciliation. Ginny's brothers would have different reactions. Some might side with Ginny, while others might think she was too hasty in leaving Harry.
Their friends would be in shock. Ron, being Harry's best friend and Ginny's brother, would be torn between loyalty to both. Hermione would probably be disappointed in Ginny and very supportive of Harry. The Weasley family as a whole would be divided. Mrs. Weasley, who loves Harry like a son, would be heartbroken and angry at Ginny. Their other friends at Hogwarts or in the Order of the Phoenix would likely gossip and have mixed feelings. Some might pity Ginny for the difficult situation she got herself into, but also condemn her for cheating on Harry.
One possible reason could be that Harry realizes he has stronger emotional and intellectual compatibility with Ginny. He might find that Ginny understands his complex life as a wizard better, especially with her own experiences in the wizarding world. Also, Ginny is more in tune with Harry's adventurous spirit, which Cho might not be as much.
Ginny would likely be protective. She loves Harry and knows about his difficult past with the Dursleys. So she would probably stand up for him right away, not tolerating any of their mean remarks.
Ginny might be in disbelief for a moment. She has always seen Harry as this heroic figure and now he's asking her to the ball. But then her natural confidence would take over and she would accept with enthusiasm. She would also tease Harry a little bit about taking so long to ask her, adding a bit of humor to the situation.