Sometimes a sychological weakness can hurt others. I am currently writing a story where one of the characters has a psychological weakness that has caused him to hurt others in the past. There's nothing wrong with him morally, which is why he isolated himself in order to keep from hurting anyone else. His want. His Need however, is friendship.
Make the book sum up. And then on the last page kill the most lovable character by the main protagonist and the protagonist likes it.<<< Have their last words be "I love you" or "I'm never leaving again" before being stabbed or shot or something