Vein Fire by Lucia Adams

After taking a cinder block to a playmate's leg and horribly disfiguring her, Matt is sent away to a psychiatric facility. Five years later, he's finally released. He returns to his hometown, and finds himself in the same circle of friends as the girl he maimed, Hannah. What follows is a haunting tale, as Matt becomes obsessed with the girl he scarred. Hannah, who has since been afflicted with low self-esteem and Borderline Personality Disorder, also finds herself drawn to the young man, and a twisted affair begins.