What does Beah mean when he writes on page 20 that, "These days I live in three worlds: my dreams and the experiences of my new life, which trigger memories from the past"?

Beah can never escape his years as a child soldier. He is haunted by those memories. By the end of the book he exists in three worlds. At night he exists in the world of his dreams and by day he exists in his new life. Both of these worlds are haunted by his third world: the memories of his war time experience.