Several things stand out, first being someone he most likely deeply cared for was killed in front of him. Most people are not comfortable watching death happen as Hollywood romances the idea of it. Second is reliving the event and having nightmares about it subjecting his mental unconscious has not fully processed or accepted the fact that she gone. Third, he left the area entirely and will not go back, quit his job which most likely is his only income source and if he did not have his parents to take care of him, he might be homeless on the streets. Cutting off any outside contact with friends and self-isolating are also warning signs.
Post-Traumatic Stress Disorder PTSD with a comorbid diagnoses of depression with the dramatic