He could also react with anger. Anger towards the dog, or perhaps towards the situation in general. He might feel that it's unfair that this happened to him and be determined to find out why. This could fuel his determination to get to the bottom of things, like if there was a magical influence behind the dog's attack.
Harry might react with fear. He could be traumatized by the experience and be constantly on edge, jumping at the slightest sound. This fear could make him more cautious in general.
At first, Harry might be in shock. He doesn't fully process what has happened. But as time passes, he could start to show signs of PTSD. He might avoid places where dogs are likely to be, or have flashbacks when he sees something that reminds him of the attack. His friends would likely try to help him through this, but it would be a difficult process for Harry to overcome the emotional impact of the attack.
One possible plot development could be that Harry develops a fear of dogs. This fear might then become a character trait that affects his actions in other situations. For example, he might be hesitant to enter certain areas where he suspects dogs could be present. Another development could be that the attack was not accidental. Maybe there's a dark wizard using the dog as a tool to harm Harry, and this discovery could lead to a whole mystery-solving adventure for Harry and his friends.
Ron would be full of anger and sorrow. He might direct his anger at himself, thinking he could have done more to protect Harry. He would probably become more reckless in his actions, trying to avenge Harry's death. His relationship with Hermione might also be strained as they both deal with their grief in different ways.
Harry may also feel a sense of adventure. Despite the situation, he's used to facing strange and dangerous things. He might start to think about how he can use this situation to his advantage, like finding out more about his parents or the secrets of the wizarding world that Sirius might know. He could be a bit excited as well as scared. For example, he might be thinking that this could be a chance to get away from the Dursleys for good.
Harry could initially be in shock. He's always counted on Hermione, so her abandonment would be a huge blow. He might feel a sense of betrayal and confusion.
Harry may also get angry. He could lash out at the person who he believes has betrayed him. For instance, if it was Ron, he might shout at him and say things he doesn't really mean in the heat of the moment. This anger would be a result of his deep - seated hurt from the betrayal.
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.
At first, Harry would likely be shocked and angry. He's used to being in dangerous situations, but being kidnapped by Fleur, someone he thought was an ally, would be a big betrayal. He'd probably try to fight back immediately, using his magic if he could.
For Hermione, it would be a huge blow. She would likely feel a great sense of guilt, thinking she could have done more to prevent it. She might become more withdrawn and throw herself into her studies even more, but also be haunted by memories of Harry. Ron would be devastated too. He might lose his sense of humor for a while and become more serious. He would also be very angry, perhaps vowing revenge if Harry was killed by someone.
Often, Harry reacts with anger. He's not one to take being cheated on lightly, whether it's in a relationship or in a competition. His Gryffindor pride kicks in, and he'll want to confront Draco immediately.
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.