As I understand Jack and Ennis there is no opposition between what they share together, wich is pure passion, and the bind they have with women. Ennis was realy in love with Alma, in the beguining at last: just look at them in their honeymoon travel in the mountain and after, in the little cabin. Thir love stumble on the question of violence, Alma is afraid (see the firework scene). Ennis believe that his desire is dangerous, that why he leaves... or rather push Alma to leave. With Cassie? it could have been, it not a simple cover, Ennis is not cynical.
Jack is realy in love with Lureen, see how they dance, how they look one to the other. Ennis and Jack do need their homosexual bind to be able to have heterosexuality... I have met bisexual men who were like that. Jake said that, in his mind, Lureen know and has always known, she is not afraid, she understand that like a way. Herself had some problem to be separated from her father... Randall, it would have been quite an other problem that why I think there was nothing or nearly nothing with Jack. Even when you are at the diet you may have a look at the menu?