What is an essential feature of Borderline Personality Disorder (BPD)?

Instability of relationships.
Borderline personality disorder (BPD) is a type of personality disorder that belongs to cluster B of personality disorders.

It is characterized by varying moods, behavior and self-image. The symptoms often result in impulsive actions, problems in relationships, self-mutilation, suicidal thoughts and actions, sense of emptiness and explosive anger.
Paranoia is an essential feature paranoid personality disorder; it is characterized by pervasive distrust and suspiciousness.

Theatricality is an essential feature of schizotypal personality disorder.
Lack of remorse is an essential feature of narcissistic personality disorder.

Instability of relationships.

Instability of social and interpersonal relationships is the cornerstone of borderline personality disorder (bpd). Constantly fighting to avoid real or imagined abandonment, bpds alternate between extremes of idealizing and devaluing those who attempt to get involved with them.

Long-term drug use is more related to a substance abuse disorder. Paranoia is an essential feature of paranoid personality disorder. Theatricality is central to a diagnosis of histrionic personality disorder. Lack of remorse may be present in antisocial personality disorder.