This song is wonderful in every way. If you listen to the song past it's Twilight meaning, here's what I got from it:.
A boy has a dream that he's committed suicide, and that his love is lost without him. When he wakes up, he sees his life in a new way, and that without her there, his life has no meaning.
He wants her to know that, just in case he can't hold on, she needs to help him hang on and give him a reason to stay.