In Shakespeare's Julius Caesar, Cassius explains to his friend Brutus,
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings." (1.2.140-141)
and certainly this remark can easily apply to Ethan Frome, who must return home from his studies in in the area of science, ironically, in order to care for an invalid mother. For, after his mother dies, Ethan has the freedom to leave, but because it is winter and he cannot depart immediately and because his farmhouse is so isolated and he is vulnerable to a woman who resembles so his mother, he becomes attached to Zeena who assumes the dependent invalid role that was once his mother's.
While the environment of Starkfield and the winter's forced isolation do contribute to Ethan's remaining in the family house, he clearly has the opportunity in the spring to resume his studies. But, he obviously has a personality fault in himself that he, too, has become dependent upon others. By feeling physically needed by the helpless women, Frome achieves a sense of maleness that he must lack otherwise. For, just as the invalid women need him, Ethan Frome needs to be the provider for them, finding some self-worth in being the bread-winner. For, after he decides to leave Zeena, he calculates the debt on the farm, etc., and decides that he cannot go afterall, almost as those he were looking for a reason to stay. Then, when he decides to commit suicide with Mattie, there is yet an ambivalence conveyed in this scene--
Just as they started he heaerd the sorrel's whinny again, and the familiar wistful call, and all the confused images it brought with it, went with him down the first reach of the road--
and it is this ambivalence, this subconscious desire not to leave, that seals Ethan Frome's state as provider to not just one, but two women.
Clearly, there is a distorted co-dependency with the characters in Edith Wharton's novel, a co-dependency that is underscored when Zeena returns from the role of invalid to resume being caretaker, the role for which she has originally been brought to the Frome farm. Ethan Frome's fate lies "not in the stars," but in himself.