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.
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.
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.
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.
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.
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 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.
In fanfiction, the 'betrayal by friends' trope often serves to create drama and character development. For Harry, it could be a shattering experience. However, it also opens the door for new alliances, like with Draco. Draco, who might have his own complex reasons, could see this as an opportunity to show a different side of himself to Harry. It could be a journey of redemption for Draco and a path of self - discovery for Harry.
He might be extremely hurt. Harry could go into a state of shock and disbelief at first. He may isolate himself, not wanting to trust anyone else for a while.
Well, one reason could be jealousy. Maybe his friends envy his fame or special abilities. Another could be misinformation. If they are fed false information about Harry, they might turn against him. For example, if someone convinces them that Harry is secretly working for the enemy.