The book is called 'This Lullaby' and it is written by Sarah Dessen.
Here's the cover:
This Lullaby is about a teenage girl called Remy who has always been sceptical about love and all matters of the heart. She is sure that love doesn't exist and anyone who believes in it is only standing to get hurt. Her mother has have 4 marriages and is on the verge of her 5th - all of which have failed and left Barbara heart broken and leaving Remy to pick up the pieces-. She has just graduated high school and is going to stanford after the Summer. She sets about finding a summer boyfriend and meets Dexter at her future step father's car dealership. He instantly feels a conection between them which Remy doesn't feel and thinks he's crazy. They end up bumping into each other all over which he says is 'fate' and that they are supposed to be together. When dexter's band plays at Remy's mother's wedding they decide to start a relationship which Remy decides is only till the end of summer. through the course of the book Dexter and Remy's relationship keeps changing and Remy changes with it for the better.
This book captured my heart and made me feel for Remy and wish she would get over her relationship issues and just let Dexter into her heart. She goes on a real emotional journey as everything around her changes. She just has to change with it. Everything works out for the best in the end and i absolutly fell in love with both Remy and Dexter. Even though Dexter is completly imperfect and Remy is obsessed with perfection and control. They balence each other out and make perfection.