Beth
Beth was the apple of Andy’s eye and the woman who Haley had a hard time believing was real. Andy told Haley from the start that she was in the US Coast Guard, which was why they never met. It’s only after Haley grows feelings for Andy that she discovers Beth is a real person.
She suspected something was up between Andy and Haley, and she tried to “harm” Haley on multiple occasions. In her goodbye episode, she reveals to Andy and the entire family that she’s been unfaithful to her fiancé. This prompts their breakup, and Haley is there to pick up the shards of Andy’s heart.