In the final scene with Jack, Ennis says that he "can't just quit this job like I used to." It was a ranching job he was talking about at that time. I took that to mean that he had been quitting jobs to run off with Jack, and it was easy to do when he had fewer obligations, like child support. So looking back at this scene, it seems that in his mind he was already oriented to his relationship with Jack, even at the expense of his family. If it hadn't been for Jack, he would have seriously considered the steady job.
That scene also alludes to Annie Proulx's stories of the disappearing West. The people who used to live there were giving way to new-type persons: urban people, salaried people, and company workers. So the scene indicates that Ennis was the last of a dying breed, unwilling for whatever reason to make that lifestyle transition.