Cathy's Book - Sean Stewart,  Jordan Weisman This book has the classic (in modern YA literature) boy meats girl, they date, they brake up, she is ticked off and decides to find out what is so strange about him.

This is an interesting book, along with the story you have draws through out due to the main character being an artist. Which is fine except where it occasionally blocks small amounts of text. But you really don't get any answers until the end of the book and it is slightly odd and written in Diary form.