One of the most ironic things my ex husband said to me six months after our divorce following a 13 year marriage was "Now you're the person I always hoped you would become." Having closed the door on the relationship, he now found someone he wanted to be with.
I don't think there is any way to put the ketchup back in the bottle. The Ennis of 1984 in "Taking Chances" is who he is BECAUSE of losing Jack, and after his stepwise growth in acknowledging and mourning Jack, the Ennis of "A Second Chance" has accepted that he loved Jack because he has accepted loving Ellery. He could not, in my opinion, have done it in isolation, he could not have done it without more relationship experience, and certainly not without a great deal of nurturing and counseling toward it.
He has the beginnings of an actual support structure and society now, that he never had at any point in the past. Growth does not happen in a vacuum. I have had the criticism leveled at my fics that Ellery is a "ready made solution" that reinforces a theory that you can't grow up and out of the closet without a partner. And that has never been my view. One cannot have relationship experience without experiencing relationships... and the greatest lack Ennis had was in forming relationships. The relationship he had with Jack was very carefully, and rigidly bounded, and with the few skills Ennis had, even alone with Jack on a desert island with plenty of food and tropical winds, he would have run into relating trouble before experiencing the growth steps he needed to get through. In my considered opinion.