I think it is an accurate statement to say that some people consider feelings of same-gender attraction to be the defining fact of their existence. There are also people who consider the defining fact of their existence that they are from Texas or that they were in the United States Marines. Or they are red-headed, or they are the best basketball player that ever played for such-and-such a high school. People can adopt a characteristic as the defining example of their existence and often those characteristics are physical.