[TOMT] [Book] A journal-type story written by a girl named Twila?

Trying to find this for my boyfriend. He read this book when he was in his early teens, so around 1998 or 1999? It was written by a girl who would write letters about her life to this guy who she was obsessed with. Then at the end of the book there was a little snippet from a newspaper saying that she had died in a car accident or something like that.

Any help would be greatly appreciated!