When one is a gay man, one seeks another gay man as a brother??
Speaking for myself, I have recognized that much of my longing for men is driven by a desire to find a fraternal figure or even a father figure--in other words, to experience a nurturing bond with another male that I have felt has largely eluded me in life. I think this is why I have felt envious of those with brothers (with the accompanying tendency to idealize the fraternal relationship), because family is family no matter what (the saying "blood is thicker than water"), whereas lovers and even friends can, sadly, sometimes come and go.
But I don't think my feelings are at all universally shared. A good friend of mine, a gay man like me and just a little bit older, who had an older sister and two younger brothers, didn't agree with my ideal of a spiritual brotherhood, and saw the roles of lover and friend as distinctly different from those of sibling or parent (again, in a spiritual/emotional sense). He saw no need or worth in conflating them, though he respected my own viewpoint and honored the fact that I shared my feelings with him. I noted that his own relations with his brothers tended to be contentious and even rancorous; he seemed to bear more sympathy and good will for his sister.
For the record, I have one older sister, and though we were not close as children, as adults I now count her as one of my best friends. I have been blessed by the presence of strong, nurturing, and engaged female figures in my family, and have been shaped for the better by their handiwork; again, it is the masculine counterpart to this that seems to remain elusive, mysterious, and desirable.