Sethe's recovery from the death of her nameless infant and the pain of her past as a slave was dependent on Paul D, a dependence which deteriorated when Beloved forced him out of the house.
Beloved's jealousy of Howard and Buggs (who survived their mother's attack) drove the boys away. After reappearing, Beloved attempted the same thing with Paul D, who was sincerely trying to soothe Sethe's pain and quiet the spirit at 124. Intent on having Sethe to herself, Beloved made it impossible to enter more and more areas of the house, effectively chasing him off after their encounter in the barn. Paul D departure is marked physically in the book by the disappearance of punctuation, which mirrors the sense of loss of reality in the text itself. Without Paul D's presence, Sethe gives herself over to Beloved entirely, surrendering to the negative past she had hitherto refused to succumb to.
In the case of Beloved, the ghost Beloved was a physical reincarnation of past adversity and Paul D represented the force that would have assisted Sethe in prevailing over her adversity.
