What are the motifs in Hold Still by Nina LaCour?

Guilt is a recurring idea in the story. In the novel, Caitlin is wracked with guilt following the suicide of her best friend. She knew her friend was often depressed, but she believed it merely to be a state of mind, instead of a clinical issue. As a result, Caitlin feels she is partially to blame for her friends' death, as she didn't realize the extent of her illness.