At first, Harry may be confused. He may try to reason with Severus, asking him why he is doing this. When Severus still rejects him, Harry could become withdrawn. He might isolate himself from others, thinking that if Severus, who he thought could be like a father, doesn't want him, then no one will. He could also start to question his own self - worth, thinking that there must be something wrong with him for Severus to reject him.
Harry might be extremely hurt. He could initially feel a sense of shock and disbelief. After all, he may have started to develop some feelings of trust or kinship towards Severus. Then, he might turn to anger. Anger at being rejected, especially if he doesn't understand the reasons behind it. He could also feel a sense of loss, as if he has been deprived of a chance at a real family connection.
Harry might be deeply hurt. He may initially be in denial, not believing that Severus is rejecting him. After all, he may have felt a strong connection. So, he could try to reach out to Severus multiple times, hoping to change his mind.
He may also get angry. Harry has a strong sense of justice and self - worth. Snape's rejection could be seen as unfair in his eyes, especially if he has started to develop some sort of positive feelings towards Snape. So, he might lash out at Snape or even try to prove him wrong by becoming more independent and successful on his own.
Harry could be initially shocked and hurt. After all, having your potential mate reject you is a very painful experience. He might start to question himself and wonder what he did wrong. Then, he could become angry. Given his Gryffindor nature, he might confront Draco about the rejection and demand an explanation.
One possible reason could be Severus' long - standing grudge against James Potter, Harry's father. Since Severus had a very difficult relationship with James, his hatred might be so deep that it clouds his judgment when it comes to Harry, who is a reminder of James. Another reason could be Severus' loyalty to Voldemort in the past. He might fear that accepting Harry as his son could put him in a difficult position with the Death Eaters or those who still hold onto the old Dark Arts ideology.
At first, Harry would be confused. He has always seen Snape as a complex figure, and the idea of being rejected as a son would be a shock. He might start to question his own self - worth, thinking that if Snape doesn't want him, there must be something wrong with him. As time passes, he could grow bitter towards Snape, but also use this as motivation to become stronger. He might focus on his friends and the positive relationships in his life, trying to move on from Snape's rejection while still carrying the pain deep inside.
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.
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.
Perhaps Severus's own self - image is one of solitude and self - loathing. He has spent so much of his life in the shadows, used to being alone and unloved. The idea of having a mate, especially someone like Harry who represents so much hope and light, is so foreign to him that he rejects Harry out of fear of the unknown and a sense of not belonging in a relationship.
Harry could be initially quite nervous. He's used to Severus being his strict professor. But as they explore Diagon, he may become more curious. He might start asking Severus a lot of questions about the different shops and the history of the place. And if Severus shows any kindness or protection, Harry could gradually warm up to him.
Harry's reaction could be a mix of fear and defiance. He's faced Voldemort multiple times, so he won't be completely helpless. He may try to understand Severus' psyche, remembering that Severus has always had a somewhat ambiguous relationship with him. He might try to appeal to Severus' better nature if he believes there is one. Harry would also be thinking about how this situation affects the overall fight against the Dark Arts and Voldemort. He might see it as a setback or an opportunity, depending on how he can turn the situation around.