A 55-year-old woman presents 14 months after witnessing her husband's sudden death from a massive myocardial infarction at home. She performed CPR until paramedics arrived but resuscitation was unsuccessful. She reports persistent, pervasive yearning and longing for her husband that dominates her daily experience. She keeps his belongings exactly as he left them, sets a place for him at dinner, and talks to his photograph each evening. She reports feeling that a part of herself died with him and describes emotional numbness and an inability to experience positive emotions since his death. She avoids the kitchen where the cardiac arrest occurred and experiences intrusive images of performing CPR when she enters that room. She has withdrawn from friends and activities, stating that 'moving on would betray him.' She denies hypervigilance, exaggerated startle response, or generalized avoidance of reminders beyond the kitchen. She does not experience nightmares about the event or flashbacks outside of the specific room. Her grief has not diminished in intensity since the first month after his death. Which of the following is the most accurate primary diagnosis?