This is a tender moment between the two cowboys. Ennis is reluctant to leave the mountain, not because he really likes watching sheep, but because he may be in love with Jack.
[Ennis cries in an alleyway.]
When Jack drives away, Ennis completely breaks down in an alleyway. It's the most intense bit of emotion he will ever express, which says a lot about his feelings for Jack. He also lashes out at a man who walks by, showing that he is uncomfortable expressing emotion, seeing it as a weakness.
JACK: Old Brokeback got us good, don't it? What are we gonna do now?
Sometimes love can be like a trap, and it sneaks up on these two men unexpectedly. That isn't a bad thing, but they don't quite know what to do with it once they find it.
JACK: Truth is, sometimes I miss you so much I can hardly stand it.
By not saying anything in response to this vulnerable line, Ennis says a lot. But what is it that he's not saying? Either Ennis doesn't love Jack as much as Jack loves him, or he's willing to let society and circumstances get in the way of his love.
JACK: Why is it we're always in the friggin' cold?
Jack is talking about the temperature, but he might as well be talking about Ennis's frosty attitude. Have you noticed a pattern here? Out of the nine quotes in this section, six are from Jack. Ennis rarely talks about love.
JACK: There's never enough time, never enough.
Jack is a dreamer, and he likes to think that given enough time, Ennis will come around and accept his love. But he realizes there's never enough time for Ennis Del Mar. That man is so slow, the mountain itself probably moves faster.
JACK: You count the damn few times that we have been together in nearly twenty years. And you measure the short f***in' leash you keep me on, and then you ask me about Mexico and you tell me you'll kill me for needin' somethin' I don't hardly never get. You got no idea how bad it gets. And I'm not you. I can't make it on a couple of high-altitude f***s once or twice a year. You are too much for me, Ennis, you son of a whoreson b****. I wish I knew how to quit you.
This is one of the movie's iconic lines, and it recalls the line about Ennis not being able to quit his job to see Jack, as if the two are equivalent, and Jack is just a job that no longer takes priority. Jack's love for Ennis is so strong that he can't toss it away the way Ennis can.
ENNIS: Why don't you just let me be, huh? It's 'cause of you Jack that I'm like this. I'm nothin'. I'm nowhere.
Not since Jack left Ennis did Ennis cry like this. And Ennis is crying again because their relationship is ending one more time. He only shows emotion when something is taken away from him.
CASSIE: Ennis, girls don't fall in love with fun.
The relationship with Cassie shows us that Ennis won't fall in love with anyone else other than Jack. But what does she mean here? What do girls fall in love with? Perhaps it's romance, something Ennis is chronically incapable of.