In general a “tragic” hero is a great man on whom the good of many depends and he is possessed of a tragic flaw which brings about his downfall. So in answering the question you have to try to factor these things in and examine Wharton’s novel for these traits. Ethan's tragedy lies in what his life could have become had he been able to free himself from Starkfield and his responsibilities there one two separate occasions. Ethan was keen to better himself intellectually. Much of his adult life is determined by chance and circumstance. This could be regarded (as in a Tragedy) as the operation of fate which conspired against him.
The timing of his mother’s death, another act of fate, effectively determines the course of Ethan’s life. Also through the operation of fate through chance and circumstance, Ethan meets Mattie Silver. Mattie’s arrival into Ethan's life intensifies the tragedy of what his life has become. The fact that he realises this is another element of the tragedy. His life is largely wasted, bogged down in duty and unfulfilled. In the manner of a true tragic hero he struggles bravely against the forces of fate, failed and ultimately endures.
In the novel "Ethan Frome," the man Ethan Frome has never had a life that was his own. He was responsible for his sick mother when she was alive. Zeena came to stay with the family to help care for his mother. He felt obligated to marry Zeena as she had cared for his mother and was a spinster. In the era of their life women without husbands had very poor lives. Zeena made sure that Ethan knew she would not have anything as she had given her youth to the care of his mother. Ethan marries Zeena.
Zeena is also sickly and is demanding as well. Ethan is once again subject to having a sick person to care for. He is trapped in the same environment.
When Mattie Silver comes to live with Ethan and his wife he finds love and beauty for the first time. He sees something other than a dark shadowy existence in a New England town. He feels joy. Mattie becomes his love and focus. Zeena finds out and orders her to leave. Ethan can not let Matti stay and so he goes to take her away, but he decides to have one last sleigh ride with her.
Ethan and Matti had experienced another sleigh ride during happier times. Ethan and Mattie are thinking back on that ride as they begin to head down the slopes. Ethan is aware that when Mattie leaves she will have a terrible life. She has no where to go. It is not directly stated but the sleigh ride is meant to end both of the lover’s lives so that neither will have to live their lives in tragedy. Instead the sled has to be steered a bit away from the tree to avoid hurting some children in its path. The sled hits the tree but not with full force.
Mattie is left and invalid and experiences terrible pain. Ethan's body is broken up and malformed. He too, will experience physical pain the rest of his life. The irony is that once again he has someone sickly to care for, but now there are two women, his wife and Mattie. They both live in his home. There is no joy once again, only sadness and obligation as well as a constant reminder of Ethan's sin. In turn Ethan isolates himself from the community and takes his punishment.
He is a tragic hero. He never had a chance for love and when he finally finds it, it is denied him. Yet, he is a good man and because he is a good man he has to live his life in torment.