The Light of Western Stars by Zane Grey

Blinded, like a wild creature, Madeline Hammond ran to her room. She felt as if a stroke of lightning had shattered the shadowy substance of the dream she had made of real life. The wonder of Danny Mains's story, the strange regret with which she had realized her injustice to Stewart, the astounding secret as revealed by Padre Marcos -- these were forgotten in the sudden consciousness of her own love.

Madeline fled as if pursued. With trembling hands she locked the doors, drew the blinds of the windows that opened on the porch, pushed chairs aside so that she could pace the length of her room. She was now alone, and she walked with soft, hurried, uneven steps. She could be herself here; she needed no mask; the long habit of serenely hiding the truth from the world and from herself could be broken. The seclusion of her darkened chamber made possible that betrayal of herself to which she was impelled.