Often, Harry could lose his trust in people, develop new skills or alliances to fight back, and maybe even question his previous beliefs and friendships. The story could take many unexpected turns.
Well, usually in such fanfictions, Harry might face a lot of emotional turmoil and have to find his way alone to overcome the betrayal and the challenges that come with it.
In some fanfictions, it could be that Harry discovers a dark secret about the wizarding world that his friends don't believe or are too afraid to accept. His friends, thinking he has gone mad, side with the established order. They then betray Harry by reporting his so - called 'crazy ideas' to the Ministry of Magic, leading to Harry being hunted.
The Ministry of Magic could also be the main antagonist in this case. If the Ministry is corrupted or under the influence of dark forces, they could manipulate Harry's friends. They might convince his friends that Harry is a danger to the wizarding world order, and his friends, being naive or misinformed, end up betraying him.
At first, Harry would be in disbelief. He would think it was some sort of joke or misunderstanding. But as the reality sets in, he would become a bit of a loner. He'd still have his sense of right and wrong, so he might continue to fight against the dark forces on his own, all the while hoping that his friends would come to their senses and realize they made a huge mistake in betraying him.
The theme of redemption also frequently appears. Sometimes the betraying friend realizes their mistake and tries to make amends. In a particular fanfic, Hermione, who had initially betrayed Harry due to a mind - control spell, spends the rest of the story trying to undo the damage she caused and regain Harry's trust. It's an important theme as it shows that even in the face of such a huge betrayal, there can be a path to forgiveness and restoration of friendship.
In such a fanfiction, perhaps Harry's friends are jealous of his newfound powers or popularity within the wizarding world. So they spread rumors about him being untrustworthy. As a result, Harry is shunned by many in the community. He has to embark on a solo journey to prove his innocence and in the process discovers who his true friends really are.
In some fanfictions, Harry could be betrayed by friends due to jealousy. For example, if a friend is jealous of Harry's fame as the 'Chosen One'. Another reason might be a misunderstanding. Maybe Harry is wrongly suspected of using dark magic, and his friends, without proper investigation, turn against him.
Harry would likely be deeply hurt. He has been through so much already, and this betrayal would be like another stab in the back. He might initially go into a state of shock, not believing that someone he loved could do this to him. Then, he would probably become very angry. His trust would be shattered, and he might lash out, not just at her, but also at those around him who he feels might have known or been involved in some way.
Well, it could lead to him seeking help from a magical healer or professor. Maybe it triggers some hidden power within him.
He would be extremely confused. Harry has always thought of his parents as heroes, and suddenly finding out they betrayed him would shatter his world view. He'd question everything he believed in.
A common plot is the misinterpretation of Harry's actions. His friends might think he's being secretive about something dangerous, like a new form of magic he's discovered, when in fact he's just trying to protect them. Another plot could be that a new character enters the story and manipulates his friends against Harry for their own gain.