how does charlie grow/mature troughout the novel?

Charlie struggles with apparent mental illness throughout his letters, but he never explicitly addresses this problem - rather, it lurks in the background of many of his accounts. At the conclusion of the novel, it is revealed that Charlie was sexually abused by his Aunt Helen when he was a child, but that he had internalized and concealed the abuse out of his love for her and as a result of his empathy for Aunt Helen's own problems as a child.