I think in the reunioin scene Jack stepped out of his truck, took one look around and decided that the Ennis he came to know and love would not settle for a cramped, small apartment over a noisy laundry and surrounded by concrete could not be his country cowboy's idea of a life. This had to be Alma's idea. Ennis's home before this , way out in the country side with his horses and potenially a ranch of his own was more Ennis. It was she who talked him into leaving I think Jack realized this early. My feeling is that Jack saw Ennis in a stifling situation with Alma. It was a *life* yeah, but what kind of life? Where the quality of that life with her? Ennis, after the divorce ended up back out in the middle of nowhere again where he felt closer to his roots. Jack felt he could offer Ennis so much more something along the lines of a much sweeter life. The three aspects mentioned by Jackster above would make Ennis whole as a person again. This could only happen for him with Jack.
On BBM Jack, even back then , had his own dreams of owning his own spread someday, perhaps this dream grew to include Ennis by the time they fell in love . He understood that ranch work and animals were Ennis's two real loves ( other than his girls) and he was'nt anywhere near having a *satisfying* life in this aspect alone.
" You and Alma, that's a life?" ,I feel he means you , Ennis, the man who came into himself with Jack on BBM, feels true love for Jack ,not Alma a man who makes love to a woman, when he knows damn well he would prefer it be Jack. Can't possibly be happy in a marriage where he is not free to let his true self shine through without having to pretend all the time. Where fantasy and pretense compensate for reality. To Jack, this no life, only an existence. He was ready to leave his own *existence* had Ennis said yes to his proposal. He understood the circumstances though living on a much higher financial level, they reap the same results. In the end it was still only their love for each other that survived everything. Jack was right all along. Sadly Ennis found out too late. My opinion.