Borderline Personality Disorder individuals cannot sustain emotional commitment. They change emotions in midstream and have difficulty holding on to feelings of love.
Love turns to indifference, estrangement and perhaps back again to love.
This dysfunctional cycle has its roots in early childhood. Borderlines lose their love for the parent of the opposite sex when the idealization of that parent breaks down. As a child, the BP experiences the opposite sex parent as being narcissistic, cruel and abusive. The child's love turns to hate and distrust. The opposite sex parent falls from the idealized pedestal and crumbles in the BP's eyes and heart.