Maybe in the fanfiction, Flash discovers Peter's identity in a very unexpected way, such as seeing Peter's Spider - Man suit by accident. He then has to decide whether to keep the secret or not. He might struggle with his own jealousy towards Peter and the newfound knowledge. If he decides to keep it a secret, it could lead to an unlikely friendship between them, with Flash helping Peter in small ways without Peter knowing it's him.
Peter might be embarrassed at first. He's been idolizing Spider - Man and now Tony, a real - life hero - like figure, knows about it. But then he realizes that Tony could be an even greater source of knowledge and support, so he becomes more open about his love for Spider - Man.
Well, Tony might be initially surprised. He could then start to use Peter's love for Spider - Man to his advantage. Maybe he'd give Peter more tasks related to Spider - Man tech, knowing that Peter would be more motivated. He might also start to train Peter in a way that's inspired by Spider - Man's abilities.
There could be a new level of trust. Since Peter has let Mary Jane in on his big secret, she may feel more special and trusted. Their relationship might become more intense as they now share this huge part of Peter's life.
The fanfiction could take a route where Flash becomes Peter's sidekick. He might start training with Peter to be more helpful in fights. This would be a huge change for Flash, from a bully to a helper.
Peter could be really nervous at first. He's been keeping this huge secret and now it's out. He might stutter and try to explain himself, saying he was just trying to protect her.
She might also be a bit angry that he didn't tell her earlier. She could feel left out or betrayed that he kept such a big part of his life from her. This could lead to some tension between them for a while until they work it out. She might make him promise to always be honest with her from then on.
Their relationship could become more strained. Aunt May might feel betrayed that Peter kept this big secret from her for so long. She might question his trust in her and this could lead to some arguments between them.
She might also be proud in a way. Peter is a hero as Spider - Man, and Aunt May has always known Peter to be a good - hearted person. Once the initial shock wears off, she could see this as an extension of his kind nature. She might start secretly helping him, like making sure he has proper meals and rest when he comes home tired from his Spider - Man duties. And she could be a great source of emotional support for Peter, which he really needs in his double life.
In some fanfictions, Mary Jane's reaction can be quite complex. She could be a bit angry at first for being kept in the dark. However, her love for Peter would likely override that anger. She might start to worry more about his safety as Spider - Man, constantly fretting when he goes out to fight crime. She could also become more involved in his superhero life, helping him keep his secret and offering support in ways she didn't before.