Personalities are like impressionistic paintings. At a distance, each person is 'all of a piece'; up close, each is a bewildering complexity of moods, cognitions, and motives.
Borderlines create the vicious circles they fear most. They become angry and drive the relationship to the breaking point, then switch to a posture of helplessness and contrition, beg for reconciliation. If both parties are equally enmeshed, chaos and conflict become the soul of the relationship.
One response to feeling abandoned is to abandon yourself.