I now believe that Ennis and Jack were both homosexual, but when I first saw the film, I sensed that Ennis was an otherwise heterosexual man who somehow fell deeply in love with a man named Jack, who I have always felt to be gay. The reason for this sense was that nowhere did I discern any sign that Ennis was attracted to any other male than Jack, and, as a gay man myself, I found this most unusual, though not conclusive evidence of any primary heterosexuality on Ennis's part.
Upon reflection, I have now come to see Ennis as an extremely repressed gay man, and so opted for 'Gay' in the poll. I do still think it possible (but unlikely) that Ennis may have been primarily heterosexual, so also opted for the category of Jack gay, and Ennis bi or straight.