When the scene from the book where Ennis calls Jack "Little Darlin" is not included in the film, I am not quite sure why it could be described as a
possible spoiler?!

However, my nick will give away my favourite scene (of the book)... Btw: BBM is part of the collection of short stories - Close Range - reading all of it will not only make you understand but also appreciate much more Ennis' & Jack's personality as Wyoming ranchers much more after reading the whole book!
Although I was not able to see the film yet, I took the liberty of glancing the scene on the internet. The scene in the film is quite different from what it is in the book (book: Jack comes up the stairs onto the landing, film: Ennis comes down the stairs towards Jack/book: their lips come together easily, film: Ennis looks around and lures Jack into the dark corner before they kiss). Like anyone would be, I was first disappointed of this. But in the film, Ennis' second daughter has a different name as in the book where she is called Francine. So I know that the film did not intend to visulise the book and therefore cannot expect to see all of it. I have also glimpsed the scene of Ennis & Jack after Ennis' divorce and the sadness of Jack - in the book you will not be made aware of Jack's feeling or reaction at all.
Back to "Little Darlin" as I know it from the book. The attraction started by percieving that Annie Proulx managed to write "everything" in just
one sentence. The attraction to the scene itself is its easiness (as Annie Proulx wrote) or inevitability (as I would say) - Ennis & Jack being like opposingly poled magnets drawn to each other, escape impossible, and Ennis, in his minimalistic way, showing, probably without even realising, his love for Jack by making him - with his daughters and horses - the most valuable item he treasures (only the Pope would see this as a symbol of the Holy Trinity). Reading it, one does not ask why Ennis & Jack are attracted to each other (gay, straight, bi - who cares) and there is nothing wrong with it.
Given all the feelings we find out about them in the book - it is hard to imagine how Ang Lee could have transformed this into a motion picture given the fact that both characters do not speak very much! In about three weeks time I'll be able to appreciate the film as well.