Just to elaborate on my earlier post, I think Ennis was blown away by Jack from the very 1st moment he laid eyes on him. The clue is that when Jack started to walk towards him, he lowered his head and hid his eyes under his hat. Ennis was rather shy, very lonely, and full of fears and neuroses so it is hard to read him, but I think he was amazed by this self-assured, friendly young man who not only possessed a lighter but also a truck and a silver rodeo belt buckle. He was so flummoxed he had to be reminded to give his last name when they introduced each other.
Then, when Jack suggested they go to a bar, Ennis didn't even walk beside Jack, he walked behind. He was further impressed by Jack's rodeo experience and knowledge of the job from having worked on the mtn the previous summer. Jack got him to open up about himself which few people had done before and when he told Jack a few details, Jack was empathetic, which also opened Ennis' eyes. Another thing that the film doesn't show but you have to imagine is the electricity between them. This is conveyed not only by what they did--sneaking looks at each other, making a big show of tying knots and mastering horses--but also what they didn't do--hiding behind their hat brims, carefully not looking at or touching each other.