Warning: this post will only make sense to those fans of One Tree Hill... and true love.
I have a theory. Maybe the comet does refer to Peyton, but maybe it isn't ABOUT Peyton.
Lucas wrote: "It was more than just a comet because of what it BROUGHT to his life: direction, beauty, meaning." This could easily mean by *cough* almost being run over by Peyton's car/comet, it brought direction to his life. Do you see where I'm going with this? By "connecting" with Peyton, he was introduced to Brooke. Luke was directed to Brooke through Peyton, right? So who's to say that the book is all about Peyton. Maybe it was really Brooke who brought meaning to his life.
Let's break this down some more: "There are many who couldn't understand, and sometimes he walked among them." The way I see it, nobody saw why he fell for Brooke in Season 1. Afterall, she was the partying cheerleader. Not many understood why Luke was so drawn to her.
"But even in his darkest hours, he knew in his heart that someday it would return to him, and his world would be whole again... And his belief in God and love and art would be re-awakened in his heart." Now let's skip a few seasons. Brooke broke up with Lucas at the beginning of season 4, mind you, his only father figure had just been murdered by his biological father, his brother had just gotten into an almost deadly accident and he just lost an old friend in a school shooting. Not to mention, the girl he loved and was in love with just broke up with him. I would have to say those are some dark times in his life, no?
Then again, it's just a theory. And a theory is no match for Mark's destructive plan; he hasn't given up on Pucas even when many of us cannot see even the slightest ounce of chemistry between the two. But no! We must be blind to not see the true and flawless love that sets upon Lucas and Peyton, yes I see it now... they are totally meant to be together. It's DESTINY!!!!!!!!! *rolls eyes*. Please.