I believe Ethan From 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.