Great posts
A part of Jack is very nurturing, we see it with his son in the tractor, interacting and having fun. Showed frustrated concern for his son's problem in school, I feel in order to really know how Jack felt about his son , the relationship between them needed to be explored more.
Both Jack and Lureen appeared to be involved in running a successful business+ Jack was pre-occupied with his love for Ennis. Problems with LD who probably influenced the boy through the years. Jack felt like an outsider in Childress, and I don't feel a proper bond was fully reached with Bobby. This would explain his willingly to leave them and get with Ennis if he'd have him
LD, apparently at some point attemtped to "buy" Jack out of the family, to leave, and Jack was actually considering it, if he could have Ennis. By the time the "older" Jack appeared, Bobby had also grown into a young man. I would be interested to know how their relationship was then, but that was not developed in the movie.
He never spoke of him , except in the reunion scene when Bobby was 8 mos. old. Perhaps he saw himself as some one seperate ,and apart ,from his family in Childress. He and Ennis were on one side, his family on the other. Two seperate realites ,as Ennis had. They were so emotionally bonded together, that niether could commit fully to any other relationship, and feel as complete within themselves. 2 cents.