If I loved a book, I wouldn't be able to finish it twice. I'd re-read my favorite parts again and again, analyze the dialogues, emotions, characteristics, author's mentality, etc., to the point of obsession. Then, I'd get sick of myself and stopped reading it. There are a lot of books that are dear to me, but I can't read them again for that particular reason.
But in general, I try not to get too attached to a book, I'll just read something well-written, fun, or thought-provoking.