Alternatively, Ginny could be very mature about it. She might respect Harry's decision, even though it hurts. She could choose to step back and give Harry the space he seems to need while secretly hoping that he will change his mind in the future.
One possible reason could be that Harry is too focused on his fight against Voldemort and doesn't want to put Ginny in danger. He might think that being with her would make her a target for his enemies.
He might be initially in shock. Harry could stand there, unable to believe what has just happened. Then he might become angry, lashing out at his mate or the situation in general. He could say things he doesn't really mean in the heat of the moment.
Ginny might be overjoyed. She could blush deeply and then give Harry a big hug, telling him she feels the same way.
Ginny might be heartbroken at first. She could retreat into herself, spending a lot of time alone in her dormitory or in secluded places around Hogwarts. She may cry a lot and avoid socializing with their mutual friends.
She might be hurt at first. Since she's pregnant, her emotions could be more fragile, and Harry's anger could really sting.
She might blush. Since Ginny has feelings for Harry, his stare could make her feel self - conscious and her cheeks turn red.
Ginny might be angry. She could feel that her brothers are interfering in her personal life and not respecting her feelings for Harry. She might confront them directly and tell them that it's her choice who she wants to be with.
On the other hand, Ginny might secretly be a bit flattered that Harry is so possessive over her. But still, she would probably try to stop the situation from getting worse and make Harry understand that he can't just go around punching people because of her.
Ginny might initially be heartbroken. She could retreat into herself, feeling betrayed and confused. In some fanfictions, she may cut off all contact with Harry immediately.
He might be initially heartbroken. Harry has deep feelings for Hermione, so the rejection could come as a shock. He could withdraw into himself for a while, feeling sad and confused about why she doesn't feel the same way.