I don´t remember how I voted, but I think I might have voted "bi". However, I must say that when I watch the movie now I definately think he is gay.
To a large extent because it´s vital to the story that he is. The story is after all about, according to AP, a homophobic society and how that affects people. If Ennis wasn´t gay...then what would be the point?
Thinking of Ennis as bi, for me, deminishes the point of the story somehow, and therefor I prefer to think of him as gay.
But then again, maybe it doesn´t matter. Gay or not, he was in love with a man and spent his life feeling unhappy because he couldn´t have the one person in the world he wanted.
But wheter he knew he was gay or not is a hard one. At least if we are talking pre-Jack. Perhaps he had felt an attraction towards men before but ignored it, or perhaps he hadn´t seen it as even a possiblity and therefor never even let himself thought about it. If you don´t event think it´s a possiblity to love a member of the same sex in that way, maybe you don´t even recognise your feelings for what they are.