What is the importance of Bella in the novel Fugitive Pieces?

Bella is important in relationship to Jakob Beer, the protagonist in Fugitive Pieces, who is a Polish Holocaust survivor. Bella was his sister. When Jakob was seven, the Nazis murdered his parents and abducted Bella. He never saw her again, and he presumed that she died in a concentration camp. Perhaps because he did not witness her death, he cannot escape his memories of her. While Jakob moves through the stages of his life, Bella is eternally a child in his mind.
Jakob was helped by a Greek scientist who was working in Poland and took him to Greece. The power of a sibling’s love combined with his survivor guilt keep Bella at the front of his consciousness. Even after he falls in love with Alexandra, Bella is always in his thoughts. His wife views this as an unnatural obsession, and their differences of opinion about this are a major contributor to their divorce. Later, Jakob meets another woman, Michaela, who is much younger. Although his preoccupation with his dead sister concerns her, she differs from Alex in being able to empathize with his loss. He can then imagine Bella as she might have been as an adult, rather than as a child frozen in time. Once this shift occurs, he frees himself and can enter into a full adult relationship with Michaela.
http://canadianpoetry.org/volumes/vol41/preface.html