What is the title (or who is the author of) a book about a woman whose ex wrote about her?

I read part of a book a while back about an overweight woman whose ex-boyfriend wrote about why he dated her (because she was fat). She got upset and that's about all I can remember. I lost the book and when I found it, I had to return it to the library so I never got to finish it (or beyond chapter one) but now I am looking for it again. Any suggestions?