The Laundry Room is where it all comes together.
I was thinking just now about how Ennis tried to "wash everything he could reach", how he tried to clean things up, make things all right, all pure and simple and acceptable. Even during the last days of the story, he threw all the horseblankets from the Coffeepot Ranch into his old pickup truck, took them into town and washed them in the car wash. Before leaving town, he ducked into Linda Higgins' gift shop looking for a postcard of Brokeback Mountain. Linda was removing a sopping wet coffee filter from her coffeepot, throwing it away. She ended up ordering a hundred postcards of Brokeback Mountain, just so Ennis could have his one. That's how I remember it anyway. Your mileage may differ.
I also remember how Ennis stuck a toothbrush in his mouth as he was packing to go off with Jack on a "fishing trip". Pawing through the closet, he sniffed a shirt or two in order to determine if they were clean enuff to take with him. And Alma, until they moved to the Riverton laundromat, had had to wash his shirts at the sink on an old washboard. Years later, she would be at the sink with Ennis again, sluicing plates, and talking about his fishing with Jack. "That line hadn't touched water in its life" she said then. And it was like the water of Brokeback Mountain called out to "its domestic cousin" just then, bringing the transformative power of nature into that little kitchen, overwhelming Ennis and causing him to threaten her with the fire of a burning bracelet. She'd overstepped his line with her line about the line.

After too short a time, it was Ennis who was on the washboard, bumping down the washboard road that zigzagged to Lightning Flat, on the welling prairie. Again, he visits a closet, again he searches for a scent remaining in a shirt. He finds only the remains of blood from a "gushing nosebleed" 20 years ago on Brokeback Mountain. Then, he finds the hidden shirt, his own shirt, "lost, he thought, long ago in some damn laundry." And he takes the shirts, takes them to his own closet. Through a few stinging tears, he says, "Jack, I swear--" as blood brothers do. What he did after that, we know little (Heath said "not much"), but we do know sometimes the pillow was wet, sometimes the sheets. Love is truly a force of nature, like the natural force of water. And like nature it is inscrutable, unknowable, inescapable, uncontrollable. All you can do is stand in awe before Nature's power and beauty and do what she compels you to do.