What was Mrs. Huntingdon's mistake in her marriage?

Mrs. Huntingdon entered her marriage with the belief that her love for her husband would be enough to help him see the error of his ways and would keep them both happy. However, Mrs. Huntingdon's love was not enough to cure her husband of his affection for alcohol or to keep him from breaking his marriage vows by having an affair with a married woman, a woman who was once Mrs. Huntingdon's friend and confidant. Mrs. Huntingdon finds her trust in her husband completely destroyed and is left to her own devices in finding a way to protect her son.