Looking for Alaska question

I believe he decided to add the before and after to show how greatly Alaska affected his life. The days before showing his transition from leaving home, finding friends, trying new things, and falling in love with Alaska. The after is,of course after Alaska's death.

Negzzz wrote: "I know this is the dumbest thing, I should have understood after I finished the book, but I'm still confused as to why John Green decided to include the before and after. I just don't understand wh..."
It is before after Alaska's death. The count starts way before he knew Alaska because he had no idea that something so life-changing was going to happen to him. You never know if someone you're close to or in love with is just going to die. The "after" part of the novel shows how the death changed "Pudge"[(?) is that his name in this one?] and how he finds enlightenment with the mysteries of humans and life.

It's before and after her death. There are moments in life that become markers. The events before and after become part of that timeline for that event, whether they're relevant to it or not. Mothers sometimes measure time by the ages of their kids. History talks about pre- and post-war life. In this book, it’s before I lost Alaska and after. I think it’s an apt and powerful device.

John Green mentions in an interview that because this book was written around when 9/11 happened, he realized that mankind defines time by the major events that happen. People around the time would talk about living in a "post 9/11" world and he thought that having a before/after timeline would stress the impact of that event.