Has anyone thought that there may have been a bit of sarcasm from Jack asking Ennis this question? Just a bit of anger. Perhaps even a dig at Ennis for choosing to marry Alma over him post-Brokeback in Signal, when he knew good and well,deep down ,his heart already belonged to Jack? Anger and frustration ,that after all that time, Ennis is still refusing to acknowledge the honest truth. Calling Ennis out on what was the mistake he and Ennis knew in marrying Alma in "63",? That Jack knew or sensed way back then ,that the marriage to any woman would'nt work? After all, it was he who sent the first postcard during his own screwed up marriage ( of which he'd had enough) knowing full well that Ennis may be married to Alma, settled ,and unwilling to rekindle Brokeback? Then being turned down again by Ennis post-divorce. Perhaps Jack knows Ennis, better than Ennis knows himself.
He knew all along that what happened with himself personally, and especially with Ennis on Brokeback was not just just some passing fancy about two friends who had some slight crush and acted on it for a few months, he knew something changed Ennis from the reluctant cowboy, he met one day in Aguirre's trailor. A mutual * meeting of the minds* in SNIT that something profound had happened to both of them that changed them forever. Many yrs. later, Ennis is still unmarried , unwilling to make such a mistake twice, yet refusing to ranch up with him. perhaps Jack thinking on account of him, Ennis cannot love anyone else , man or woman that way ever again. Maybe after 20 yrs. he still holds out for hope that Ennis will come to his senses and see that he might as well ranch up together, for that is the only way Ennis will be truly happy... fearful and cautious, but happy.
I agree with all the above posts that Jack was indeed probing to find where he stood. He had to ask for the many different reasons posted, finally he just says he can hardly stand living apart from Ennis, but is met with silence, though I feel he knows by now what Ennis's problems are. Ennis fears what Jack represents about who he feels he is himself, and Jack knows there's no way out of loving Ennis despite it. Thanx