Borderline Personality Disorder (BPD) is characterized by pervasive affective instability and emotion dysregulation. This paper introduces the Core Emotion Framework (CEF), a structural-constructivist model integrating affective neuroscience, embodied cognition, and strategic emotional regulation. CEF conceptualizes psychopathology as Emotional Rigidity—maladaptive fusion of core emotions—contrasted with the therapeutic goal of Emotional Flexibility. The framework is critically compared with empirically validated treatments, Dialectical Behavior Therapy (DBT) and Schema Therapy (ST), highlighting mechanistic differences: DBT targets behavioral skill deficits, ST addresses maladaptive schemas, while CEF intervenes at the moment-to-moment construction of emotion via conceptual restructuring, predictive updating, and detangling techniques. The analysis underscores CEF's theoretical promise in addressing BPD's hypersensitivity and relational instability, while emphasizing the primacy of established treatments until empirical validation is achieved.