Kayleigh: Hurry up, I want a quickie before school!
Jason Treborn: You can't change who people are without destroying who they were.
Kayleigh: Nothing's all better, okay? Nothing ever gets better!
Kayleigh Miller: Where'd you learn those new tricks?
Evan: What? It... It wasn't... Weird... Was it?
Kayleigh Miller: Yeah, if you call multiple orgasms weird!
Dr. Redfield: Just think of your mind as a movie, you can pause, rewind or slow down any details you want.
Mr. George Miller: Take off your clothes, just like we do at bath time. You too, Evan.
Answer: The point of the movie was that, no matter what he did and how he tried to change things, they always ended up bad. If he went back and did that, something unforseen would have happened to make things terrible. Evan realized that everything bad that happened to them was because of him. He then decided the only safe way to make things right is if he just took himself out of their lives all together. That's the logic the filmmakers went by, if you don't want to accept that, then you will just have to consider it a plot hole.