Well, it would change him a great deal. He'd probably go through a period of intense grief. This could lead to him isolating himself from his friends like Ned. However, he'd also realize that Aunt May would have wanted him to keep being Spider - Man. So he'd start to focus more on the big - picture threats to the city, rather than just small - time crime. His motivation would shift from just doing the right thing to honoring Aunt May's memory.
Peter might be initially very nervous. He's been keeping this huge secret from Aunt May for a long time, and now that it's out, he's worried about how she'll react. He might stutter and struggle to find the right words to explain himself.
Well, a really cool 'Peter Parker is Spider - Man' fanfiction could involve him traveling to an alternate dimension where he's not the only Spider - Man. He could learn new skills and ways of being a hero from the other versions of himself. Some fanfictions might also explore what would happen if Peter lost his powers temporarily and had to rely solely on his wits and martial arts training (which he surely has). It would be a great character - building story for him.
Well, it happened when Peter was on a school field trip. A radioactive spider bit him, and that's what triggered the transformation. His newfound powers led him to take on the identity of Spider-Man to fight crime and protect the innocent.