According to the Oxford Dictionary, in literature, a tragedy is "a play dealing with tragic events and having an unhappy ending, especially one concerning the downfall of the main character."
As the life of Ethan Frome unfolds, through the musings of the narrator, one comes to understand that Ethan's life truly illustrates that definition.
His youth was spent caring for his injured father and aging mother. Rather than pursuing his own pathway in life, he is saddled with the family farm. Though he does marry, his wife has her own ailments and she requires much assistance. That assistance comes from Ethan and the wife's female cousin, Mattie. Ethan and Mattie are caught in the web of unrequited love. Their only hope is that, upon their eventual death, they will finally be together.
When the sickly wife sets forth a plan to separate Ethan and Mattie, they plot to end their lives and hasten their time together in eternity. Tragically, their plans go awry.
The tragic story of Ethan Frome, which started with his father's injury, ends with Ethan and Mattie's own injuries. They ARE to be together for eternity, under the constant care of Ethan's, now recovered, wife.