The Second Virginity of Suzy Green by Sara Hantz

() This main character of this book moves to a new town and a new school, where she tries to re-attempt her life. She models most of her 'new self' off of a deceased sister that she blames herself for the death of. She is instantly accepted to the 'in' crowd, and lies her way to be accepted even further. Unfortunately, a past boyfriend shows up who knows the truth - his presence threatens the position she's made for herself.
As you can guess, she eventually reverts back to who she was - finding that being anyone else is not fulfilling. (I'd say the ending is a little too obvious - which insults my intelligence.) It makes you question responsibility, right and wrong, forgiveness, and attraction - if you weren't already.