“When the idealized person finally disappoints (as we all do, sooner or later), the borderline must drastically restructure his strict, inflexible conceptualization. Either the idol is banished to the dungeon or the borderline banishes himself in order to preserve the “all-good” image of the other person. This type of behavior, called “splitting,” is the primary defense mechanism employed by the borderline. Technically defined, splitting is the rigid separation of positive and negative thoughts and feelings about oneself and others; that is, the inability to synthesize these feelings. Most individuals can experience ambivalence and perceive two contradictory feeling states at one time; borderlines characteristically shift back and forth, entirely unaware of one emotional state while immersed in another.” 


Excerpt From I Hate You--Don't Leave Me Jerold J. Kreisman &amp; Hal Straus https://books.apple.com/us/book/i-hate-you-dont-leave-me/id397031176 This material may be protected by copyright.