**Core Concept**
Dependent personality disorder (DPD) is a mental health condition characterized by a pervasive pattern of dependent behavior, including a need for others to assume responsibility for major areas of life, fear of separation, and helplessness in daily life. This is often accompanied by anxiety, low self-esteem, and difficulty in making decisions.

**Why the Correct Answer is Right**
The patient's symptoms, such as difficulty in work, decision making, and socializing without her ex-partner's help, indicate a need for others to assume responsibility for her life. Her history of low self-confidence, fear of rejection, and abandonment also support this diagnosis. Furthermore, her brightening easily when interacting with her ex-partner suggests that she may be people-pleasing and seeking approval from others. This pattern of behavior is consistent with the diagnostic criteria for dependent personality disorder.

**Why Each Wrong Option is Incorrect**
**Option A:** Acute stress disorder is typically characterized by symptoms that develop within a month of a traumatic event, such as flashbacks, nightmares, or severe anxiety. This patient's symptoms do not appear to be related to a traumatic event.

**Option B:** Major depressive disorder is characterized by a persistent feeling of sadness, loss of interest in activities, and changes in appetite or sleep. While this patient appears anxious and sad, her symptoms are not severe enough to meet the diagnostic criteria for major depressive disorder.

**Option C:** Borderline personality disorder is characterized by a pattern of unstable relationships, emotional dysregulation, and impulsivity. This patient's symptoms do not suggest the level of emotional dysregulation or impulsivity seen in borderline personality disorder.

**Clinical Pearl / High-Yield Fact**
Dependent personality disorder often co-occurs with other mental health conditions, such as major depressive disorder, anxiety disorders, or substance use disorders. It is essential to assess the patient's relationships, coping mechanisms, and self-esteem when evaluating for dependent personality disorder.

**✓ Correct Answer: D. Dependent personality disorder**