This was a very popular film when it came out, largely because it featured two gay cowboys played by two heterosexual actors, Jake Gyllenhall and Heath Ledger. It focuses on the immensely complex relationship that is formed between two cowboys who work one season looking after sheep in the fictional area of Brokeback Mountain in the state of Wyoming.
Ennis is a very repressed individual who finds it very challenging when Jack makes sexual advances at him one night as they look after the sheep together. He responds however, and it is clear that the two form a relationship that is built on love and physical attraction. However, Ennis is greatly concerned about the way in which homosexuality is viewed by the society around him, and as a result when they both leave the job, they have a fight and he leaves to get married to his sweetheart.
The film charts their relationship over the next twenty years as they both get married and have families and live lives that are both happy and unhappy in different ways, largely because they are unable to publicly acknowledge their relationship. After Jack is killed in a supposed accident, he travels to visit his parents, and sees that Jack has kept the shirt that he wore when he had a fight with Ennis so long ago. Ennis keeps the shirts and it is clear that he loved Jack all along.