In some fanfictions, it could be due to a long - hidden family secret. His parents might have had a past that they were ashamed of or a debt they had to pay, and unfortunately, Harry became a part of that repayment which led to the perception of betrayal. They could have made a deal with a dark force before Harry was born, not realizing the full implications it would have on their son.
In such a fanfiction, perhaps the parents were forced to betray Harry due to some dark magic or a powerful enemy threatening them. Maybe they had to give up Harry to save the wizarding world from an even greater evil.
If Harry's parents are the ones who betrayed him, they could be considered the main antagonists in a sense. They created this false image of themselves as loving parents when in fact they had ulterior motives. Another possibility could be a character who was in on the parents' plan and now is trying to cover it up or continue the malicious work they started. Maybe it's an old acquaintance of his parents from their days at Hogwarts who is now out to stop Harry from finding out the truth.
Well, perhaps in the fanfiction, it shows that Harry's parents made a deal with Voldemort before their deaths. They promised to hand Harry over in exchange for something, like power or protection for themselves. But then things went wrong and they ended up dying, still leaving Harry feeling betrayed as he discovers this truth later. It could also be that his parents were actually working against the Order of the Phoenix all along and Harry was just a pawn in their real plan.
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.
At the start, Harry would be stunned. His whole life has been built on the idea of his parents being heroes. When he realizes they betrayed him, he would be heartbroken. He might go on a journey to find out the real motives behind their actions. Along the way, he could become bitter and vengeful. However, he might also find some inner strength and decide to rise above the betrayal. He could use it as a motivation to break free from the shadows of his parents and create his own path, but not without a great deal of emotional turmoil first.
In some fanfiction, the idea of Harry Potter being betrayed by his parents might be justified through a complex web of magic and prophecy. Maybe the parents thought sacrificing Harry was the only way to save the wizarding world from a greater evil. However, this goes against the essence of their characters in the original books.
Maybe they were forced into it by some dark magic or a powerful dark wizard. They could have been blackmailed into betraying Harry to save their own lives or the lives of others they cared about.
One popular fanfiction might be 'The Dark Truth of Betrayal' where the author explores a scenario where Harry discovers some long - hidden secrets that make him question his parents' actions. Another could be 'Betrayed by Blood' which delves into a world where Harry is led to believe his parents had a more complex and perhaps less noble side. There's also 'The Illusion of Parental Purity' where magic and false memories play a role in Harry's discovery of his parents' supposed betrayal.