This is a good way of looking at the situation I think. Maybe Jack also realized (almost immediately) that Ennis would feel very, very bad about the punch... because after all Jack felt very, very bad about giving Ennis the bloody nose (even if it was more accidental). In certain ways, there is some nice symmetry here.
It just seems that Jack is somehow able to get over things... lots of things... and just keep going. He doesn't seem like he's one to carry a grudge (much).
The more I think about this, the more I think the “punch” is emblematic of Jack and Ennis’ relationship. Unintentionally or not, Ennis delivers a “punch” to Jack over and over. The first actual punch is symbolic of the pain Ennis is internalizing but is unable to express verbally. Post mountain, however, Jack is constantly getting “beaten up”. Think about it …. when they finally see each other after four years, Ennis refuses to have a life with Jack. This is the theme for the rest of their lives. The one time when Jack thinks Ennis has reconsidered is after Ennis’ divorce. Jack travels 14 hours only to find that Ennis is still unable to give himself to Jack. That scene is a turning point. Yes, Jack doesn’t hold a “grudge” only because he loves Ennis so deeply and can not imagine a life without him. At that moment Jack knows that the best he’ll get is the few “fishing” trips once or twice a year. It is a devastating moment. It doesn’t mean that Jack doesn’t try ….
“Maybe it’s time you moved outta there. You know, set yourself up somewhere different. Maybe Texas.” As usual, Ennis rejects the idea. By that point, however, Jack is not as affected by the pain. It has become a pattern and Jack knows it will not change.
I think Jack might be mainly surprised and a little flattered at that moment in the motel when Ennis demonstrates that he's been worrying about that punch for 4 years. Ennis is cute here because he really reveals how much he's been worrying about Jack. Not only was he worried that Jack might have hurt feelings over the punch, but he's also clearly been very worried about Jack winding up in the army. In a way, that kind of concern over Jack's well-being is very romantic... and I think Jack gets this as he's lying there.
The motel scene is wonderful because it
is so intimate and honest. This scene shows how much they truly love each other. It is one time (albeit not the only time) where Ennis makes himself vulnerable. He is painfully honest when he says,
“I’m stuck with what I got here.” The expression on his face is one of pure sadness. It is obvious throughout that scene how much Ennis has missed Jack. Look at how many times Ennis caresses Jack’s arms. It is lovely. After that, however, Ennis’ fears overtake his feelings for Jack. Thus begins the pattern of hurting Jack over and over again.