An 18-year-old female exhibits fears of abandonment and recurrent self-harm. She is likely suffering from:

The scenario of an 18-year-old female exhibiting fears of abandonment along with recurrent self-harm is indicative of borderline personality disorder. This condition is characterized by a pervasive pattern of instability in interpersonal relationships, self-image, and affects, alongside marked impulsivity. Individuals with borderline personality disorder often experience intense emotions and have difficulty regulating them, which can lead to self-harming behaviors as a coping mechanism.

Fear of abandonment is a hallmark feature of this disorder, where individuals may go to extreme lengths to avoid real or imagined separation from significant others. The combination of these symptoms strongly points to borderline personality disorder rather than the other listed disorders.

Seasonal affective disorder primarily involves mood changes with seasons, not the specific relational and self-destructive patterns demonstrated here. Reactive attachment disorder typically arises from situations involving severe neglect in early childhood, leading to challenges in forming healthy relationships, which does not align with the described age and symptoms. Bipolar disorder is characterized by mood swings, including depressive and manic episodes, but it does not specifically include the fears of abandonment or recurrent self-harm as central features.

Therefore, the symptoms presented are most accurately associated with borderline personality disorder, making it the most appropriate diagnosis.