"Friend that more word you spoke in the past two weeks", Jack said to Ennis on Brokeback, Ennis replied, "Hell, that more I spoke in a year", That always intrigued me. Why at that moment did Ennis feel secure enough with Jack to speak freely about himself, and why with him? Alma was already in his life, but Jack was someone he felt he can be open with.
We can say that Ennis may have liked Alma, something of affection for her, but Jack was more becoming a person he was drawn to, enough that he began to let his guard down with, and enough that a trust was beginning to form.
And Jack recognized this moment, because like Ennis a connection to someone else, another human being was being made. Something that both men craved and needed and found in each other, apparently no one else up until that moment touched.
So no matter if Alma was there or not there was a part of Ennis that Jack could reach. IMO.