A 58-year-old female presents 14 months after the death of her husband of 30 years from pancreatic cancer. She reports persistent, intense longing and yearning for her husband that occupies most of her waking hours. She describes feeling emotionally numb and detached from others since his death, has been unable to return to her hobbies or social activities, and states she feels her life has no meaning or purpose without him. She avoids any reminders of his death, including the hospital where he died and friends who visited during his illness, while simultaneously being unable to stop thinking about him. She reports persistent difficulty accepting that he has died, sometimes setting a place for him at the dinner table. She has lost 20 pounds without trying and has not returned to work. She denies suicidal ideation, psychotic symptoms, and substance use. Her PHQ-9 score is 12. What is the MOST likely diagnosis?