Like others here, I don't believe Jack's love was "wearing out". As Southendmd has pointed out, Jack doesn't say that he's quitting Ennis but "I wish I knew how to quit you". In this moment of emotional exasperation with Ennis, Jack may well wish to be quit of Ennis but, as he acknowledges, he doesn't know how. I suspect that once things have settled down, all thoughts of even trying to quit Ennis will have disappeared.
Nevertheless, this is an important scene as it is directly connected to the second tent scene and, because of this link, we can look back over the whole of the movie and possibly forward as well.The link is provided by Jack. In the second tent scene, as Jack starts to hold Ennis, he murmurs to him "it's all right...it's all right". In the quarrel scene, as Jack once more takes Ennis in his arms, he again says to him "it's all right...it's all right". The difference , however, is that after the second "all right", Jack adds "damn you, Ennis". However, Jack's addition of"damn you" here is not, I think, a suggestion that he's about to walk away but an expression of emotional frustration that something that started in that second tent scene has never, for Jack at least, reached a satisfactory conclusion even after nineteen years.
However, if the quarrel scene is a way of looking back, it also leaves open the question of what will happen next. Will anything change?i I think it's possible that it isn't Jack who changes but Ennis When Ennis sends Jack that final postcard suggesting that the two of them meet up at Pine Creek on Nov. 7. it looks as though this is the first time that Ennis has been the initiator in arranging their meetings, This, I think, is significant. Also, he's had the whole summer to think things over and recognize that Jack has even mentioned the notion that he might quit Ennis. Then Ennis's family obligations for his daughters are lessening. By the time of the quarrel scene, Alma Jr is at least seeing her first boyfriend, Troy, if not her husband-to-be, Kurt. Jenny can't be far behind. If his child support payments stop at 18, then he'll have stopped paying money for Alma Jr by the time of the quarrel scene and the same will be true of Jenny in a year or so. As well, in society, things are changing. "83 is not '63 and by '83, gay men are integrating a little more easily into society compared to twenty years ago. Even Ennis must be vaguely aware of this.
For all these reasons, I believe that Ennis, at that November meeting, might well have been prepared to offer Jack more of that "sweet life" than he had ever been prepared to before. If I'm right, of course, the tragedy is, that all of this came a few months too late.
