Why does Elie feel ashamed? What does he regret?

Though Eliezer feels relieved when his father dies, it is clear that this emotion is merely a momentary one that he later deeply regrets. For after his father's death, Eliezer's life in the concentration camp also ceases to really exist: "I have nothing to say of my life during this period. It no longer mattered. After my father's death, nothing could touch me any more." The narrative ends rather abruptly after his father dies because to Eliezer, there is really no more story to tell. His story of life at Auschwitz and Buna has been one in which he and his father struggled together to survive, and after he dies, details become irrelevant.