Why does the marshall deceive miss fairchild?

The marshal deceives Miss Fairchild to maintain the illusion of a respectable and successful life that he believes she expects from him. He is aware of her higher social status and wants to preserve her dignity by hiding his true circumstances as a lowly lawman. This deception stems from his desire to protect her feelings and prevent any embarrassment, ultimately reflecting his deep affection for her. The situation underscores themes of class disparity and the complexities of personal relationships.