City vs. Country
The use of landscape in Brokeback Mountain creates a juxtaposition between circumstances. The city represents the model of masculinity that Ennis must adhere to, repression, work, heteronormativity, and his "normal" life. Viewers should note that when Ennis returns from his calm summer rendezvous on the mountains, his busy wife and screaming children greet him and create a noisy, bustling scene; this produces a discrepancy between both occurrences because the brief moments on Brokeback with Jack are where Ennis can honestly be himself. Their time together features beautiful, serene lakes and countryside, calming music, and silent expression.
The contrast between landscapes also shapes Ennis' personal views on city life, which is how he must conform to rigid rules and exhaust himself with displeasing farming gigs. In nature, he is free and allowed to act in ways that aren't typical of conservative Wyoming men in the 60s -- or men in the 60s in general!
Yearning/Desperation
The themes of desperation aren't subtle, especially with Jake Gyllenhaal's character, Jack Twist. Many viewers assume that Jack loves Ennis more than Ennis loves Jack, but that's false if you consider their subsequent tryst four years after Brokeback. Before Jack can ask a simple "How the hell are ya?" they embrace, and Ennis initiates a smoldering kiss; this scene merely shows how much they miss each other, their love is still as strong as it was, but their desperation amidst their formal lives tears them apart at the seams. Both appreciate each other's presence, but Ennis -- of the two -- experiences the most repression as Jack is vehemently open to settling down.
Jack once tells Ennis on one of their camping trips, "Sometimes I miss you so much I can hardly stand it." This quote shows the yearning that Jack goes through in his daily life; while not always apparent due to his heteronormative performance to please others, it's there, and it's never stopped since Brokeback.
Both must "stand" their mundane lives, having to hide and put on a show while living with such intense feelings toward each other that they'll never be able to openly show in their lifetime, which creates a great deal of yearning and desperation; this is the tragedy of Brokeback Mountain.
(Toxic) Masculinity and Homophobia
Toxic masculinity is most prevalent in Ennis. His rigid adherence to American ideals of masculinity (stoicism, heteronormativity, aggressive behavior, etc.) poisons him and others around him. He thinks that clinging to this ideology will save him from his repressed homosexuality when in actuality, it only kills him inside more. His expression of frustration with his circumstances kills his marriage and connection to his children. It's not entirely his fault, but many believe Ennis could've lived a happier, healthier life if he had just thrown out these overdone standards and let himself thoroughly enjoy the twenty years spent with his lover.
His stoicism creates a rift between him and his friends and family; he bottles up his emotions until he finally releases them with yells, threats, fists, and swears, which is especially evident when Ennis threatens two crude men at a 4th of July celebration; this scene serves as his last saving grace to being completely emasculated, Ennis is trying to show himself and others just how "manly" he can be. Ennis feels emasculated because society and the American masculine ideology poison him into thinking that being with a man makes him less of a man, and it's not only that, it's people's general reaction to homosexuality like when his ex-wife, Alma, acts in disgust when confronting Ennis about his affair with a man. All in all, homophobia and toxic masculinity work hand-in-hand to suppress the free expression of men.