Jack was love, in spite of everything Jack knew how to love, I guess that's why I lean little towards him. In the film, he was the one that caught the scorn Aguirre, and didn't mentioned it Ennis. In the bar scene where he tried to pick up the rodeo clown, he was rebuffed, and the look over his shoulders after him, broke my heart. When he first met Lureen you could see he was searching for something when he danced with her, and the scene in the car made me laugh, but that was Jack, sensitive, needing, open and wanting to give all the love and passion he had to someone.
Who did he want? He wanted to give to Ennis, he was the one he truly loved, and wanted, but Ennis made it so hard for him.
Jack put himself out there for good or ill in world, and Ennis couldn't or wouldn't understand this. Jack's love was deep, it flowed freely to him, just like the rivers and streams of Brokeback.
Ennis at any time could drink of it, and be protected by Jack from all his fears. I could see Jack telling Ennis , "Friend, been there, done that." "I know what it's like out there."