Bang by Barry Lyga

Sebastian Cody did something horrible, something no one not even Sebastian himself can forgive. At age 4, he accidentally shot and killed his infant sister with his father's gun. Now, ten years later, Sebastian has lived with the guilt and horror for his entire life. With his best friend away for the summer, Sebastian has only a new friend, Aneesa, to distract him from his darkest thoughts. But even this relationship cannot blunt the pain of his past. Read a sample.