People can have bipolar and have a personality disorder--in this instance, borderline.
Diagnostic criteria for borderline personality disorder
a pervasive pattern of instability of interpersonal relationships, self-image, and affects, and marked impulsivity beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:
(1) frantic efforts to avoid real or imagined abandonment. Note: do not include suicidal or self-mutilating behavior covered in criterion 5.
(2) a pattern of unstable and intense interpersonal relationships characterized by alternating between extremes of idealization and devaluation.
(3) identity disturbance: markedly and persistently unstable self-image of sense of self
(4) impulsivity in at least two areas that are potentially self-damaging (e.G., spending, sex, substance abuse, reckless driving, binge eating). Note: do not include suicidal or self-mutilating behavior covered in criterion 5.
(5) recurrent suicidal behaviors, gestures, or threats, or self-mutilating behavior
(6) affective instability = due to a marked reactivity of mood (e.G., intense episodic dysphoria, irritability, or anxiety usually lasting a few hours and only rarely more than a few days)
(7) chronic feelings of emptiness
(8) inappropriate, intense anger or difficulty controlling anger (e.G., frequent displays of temper, constant anger, recurrent physical fights)
(9) transient, stress-related paranoid ideation or severe dissociative symptoms
now, for the day-to-day stuff:
a person suffering from bpd is incredibly egocentric, everything in their lives has to be geared towards them, and they always have to be right. By creating the above situation they achieve the following aims:
they are always right, and the non is always wrong. Their friends reinforce this, because of the faulty perception these friends have of the non.
By making the non the bad guy, the person suffering from bpd becomes the victim and will receive sympathy from their friends, boosting their ego, and self belief that they are right.
By controlling the non's life, the non is made to believe that they are wrong. With no countering opinion available, even the strongest person will be ground down.
When the non tries to break this control, a confrontation will erupt. The non is then accused of being the aggressor and of being the bully. This is used to reinforce the "i'm right, you are wrong" mind set and the external perception that the non is a bad person.
Confrontations are often staged and managed. The non is either isolated from supporting witnesses, or the bpd sufferer allows witnesses only when they can control the perception of the witnesses against the non.