Why does Holden keep repeating Allie don't let me disappear?

Holden repeatedly says "Allie, don't let me disappear" in J.D. Salinger's "The Catcher in the Rye" because he is haunted by the loss of his younger brother, Allie, who died of leukemia. Holden is struggling with feelings of isolation and alienation, and he fears losing his connection to his brother and his memories of him. By repeating this phrase, Holden is expressing his desire to hold on to his past and not lose himself in the present.