I think the SNIT is absolutely crucial for a viewer's understanding of the depth of their relationship.
Ennis woke in red dawn with his pants around his knees, a top-grade headache, and Jack butted against him; without saying anything about it both knew how it would go for the rest of the summer, sheep be damned.
As it did go. They never talked about the sex, let it happen, at first only in the tent at night, then in the full daylight with the hot sun striking down, and at evening in the fire glow, quick, rough, laughing and snorting, no lack of noises, but saying not a goddamn word except once Ennis said, "I'm not no queer," and Jack jumped in with "Me neither. A one-shot thing. Nobody's business but ours." There were only the two of them on the mountain flying in the euphoric, bitter air, looking down on the hawk's back and the crawling lights of vehicles on the plain below, suspended above ordinary affairs and distant from tame ranch dogs barking in the dark hours.
^ The last sentence in this snippet hints at the emotional depth of their relationship, but it would be difficult to replicate the effect in film, given the stoicism of the characters (which is much greater in film-Ennis as opposed to book-Ennis). We especially needed a breakthrough scene like that after the "I ain't queer" conversation, in which Ennis seemed impassive and Jack almost heartbroken.
