Book 1 the beginning

Today i started reading my book for the project. This book started off not how i would expect. Katie falls in love with a man named Matt. Well its turns out that Matt is married and has a kid named nick. The story then goes into detail about Katie and Matts relationship and when she found out when he had a wife. She recieves a diary from Matts wife with a note attached that reads this will explain things better than i ever could.