I believe Ethan Frome lost control of his life when his mother died.
After his mother's funeral, Ethan did not want to be left alone on the farm,
so he asked Zeena to stay with him. At first, Ethan enjoys her company.
However, Zeena soon becomes a nuisance to Ethan, and prevents him from
becoming an engineer in a large city. After being married a year, Zeena
becomes sick herself, and the only time she talks to Ethan is to complain or
show her discontent.
After Mattie comes to the farm, Ethan does not love Zeena at all. He
thinks the only pleasure she has left is to inflict pain on him. Since Zeena
is a burden on Ethan, he naturally wants to improve his life. The reason he
does not have control of his life is because he is married to Zeena, and he
is not brave enough to go away with Mattie.
The reason he is married to Zeena
is because his mother died. Since Zeena is why Ethan does not have control of
his life, and Ethan married her because his mother died, the point in time
when Ethan lost control of his life is when his mother died.
I believe Ethan could have changed the direction of his life if he had
gone away from the farm to marry Mattie. The reason he did not have control
of his life was because he was married to Zeena. If he would have married
Mattie and left Zeena, he would not have been in the sled accident, and
consequently, he would have lived a much happier life with Mattie.
The second way Ethan could have changed the direction of his life is if
he would have sold the farm and never have married Zeena. This would have
saved him many years of problems and unhappiness. He would never have met
Mattie, which means he would never have injured himself in the sled accident.
If he would have lived in another town besides Starkfield, he might have been
an engineer and married a woman who would treat him better than Zeena ever
did.