I think this is an important issue, both for understanding BBM, and also for understanding real-life long term relationships, and one that may be discussed tastefully and discretely.
I was working for a year or so with a man in his 40s who had been gay all his life. I knew him well enough to ask him various questions which he was glad to answer. One question was, "In the average longterm relationship, who does what to whom?" He answered that that there are rare couples where one is always one role. Then he giggled and said, "For the majority of couples, each parterner takes turns in all conceivable roles. Its all so darn much fun, who would want to miss out on any of it!"
He did share with me that one of his early experiences was with a man who was so forceful, that it caused him to bleed. He made the man stop and leave. His partner could not understand why he never wanted to see him again. He sustained such an injury, that for the rest of his life, there was some tissue that was noticably in the way. Yet he never went to a doctor for the injury.
I once had occasion to talk to a surgeon who regulary treated problems of the large intestine. I asked him if, in his practice, he often saw injuries caused by sexual activity. His face became very somber, and he said, "Oh, I have seen patients who have literally destroyed themselves."
There was one famous political figure in New York, who died of AIDS within the past 10 years. I cant remember his name. He wrote a biography of his life. One point that he made was that he had only once in his life been the receiver, and it was painful for him, so he never repeated that experience, but for the rest of his life participated only in orally. His point was that he did contract AIDS from the oral sex, and therefore, it is a myth that it cannot be contracted orally. Obviously there are people who choose for one reason or another, to restrict their sexual activity to oral practices.
Obviously, people who choose to see Brokeback Mountain, who are not gay, may be quite ignorant of what takes place in a gay or lesbian relationship. While strictly speaking, it should not be necessary to have such an understanding to appreciate the movie, yet still some people may be curious, and a better understanding of such things may enhance they enjoyment of the movie and even promote greater tolerance among the straight community.
You know, I have two cousins, brother and sister, who grew up and lived all their lives on a dairy farm. The brother is 15 years older than my 58, and the sister is about 5 years older. She married a man and had a daughter with him. It was not her first marriage. He was a house and barn painter by trade, a very manly and personable fellow. But he was secretly bi-sexual. She live with that secret for years and told no one. Her husband got into trouble with drugs and alcohol, and got into serious debt. They divorced, and for spite, he began to flaunt his now openly gay lifestyle in the small farm town where everyone knew everyone else. When asked how she had felt during the marriage, she said it was ok as long as he always came back to her. I asked her brother, my cousin, how old he was when he realized that there are men who have sex with other men. He said he did not know that until he was 30, and just could not understand it.