One of the reasons that I made Ellery such a different person... physically, psychologically, professionally (and sexually) is because my own philosophy about moving on and loving again is not about "replacing" people. Jack cannot be replaced. Nor could Ennis have loved Ellery unless he had first loved Jack, and lost him so tragically. None of what happened in Laramie could have happened, had Ennis met Ellery first... because they lived in different worlds, and because the Ennis that refused Jack could not have accepted Ellery before Jack died, and Ennis went through his vale of mourning.
For me, the biggest problem of reading and seeing "Brokeback Mountain" was Ennis remaining behind, alone in grief, without his nature as a homosexual man having unfolded. And in fact, his ability to respond to Ellery is because he is so different. I think if he had met someone who looked like Jack he might have run back to Junior's sitting room and never ventured out. It was his capacity to love Jack that gives him the capacity to love Ellery, and in my own experience as well as that of others, it is this capacity to love deeply that allows someone who has loved and lost, to move on, because the impulse to love another and embrace him is a capacity that is not limited to a single person at a single time, but can be extended to family, children, friends, mentors, and yes, to a new lover.