To quote Jammie Price, from "NAVIGATING DIFFERENCES: Friendships between Gay and Straight Men",
[Since] "being a man is" highly valued in a patriarchal context, signifying gender with other men becomes one way for men to compete for power privileges and resources. Men come to value self and other men for their ability to be a "man". In any given situation, men assess their masculinity in relation to other men and strategize actions based on those perceptions. Through this process they gain a sense of self-worth and relative standing. Hence, many men see interactions with other men as "character contests", stages on which to assert their masculinity. Those who assert their masculinity the best receive the highest regard, and accordingly, the most power and privilege among the men in the interaction.
The culturally ideal or "hegemonic" way that men signify being men in the United States today is to (1) display an ability to control, compete, and produce relative to other men, particularly at work; (2) subordinate women and reject effeminacy; and (3) express heterosexual desire. Being physically fit and of moderate size also help men to signify masculinity. The better or more a man demonstrates some or all of the above characteristics, the more masculine he seems to himself and others, [while] failure to demonstrate some or all of the above characteristics becomes the ground for men to devalue another man. (Numerous references omitted)
In her fascinating book, the author shows that for very many straight men, a friendship with a gay man is much deeper than their friendships with other straight men, because they are not competing. They can trust their gay friend with things they would never tell their straight friend. For many of the gay men, though, their friendship with the straight man is less valuable than their friendship with other gay men, because for us it is hard to trust straight men. We have suffered at their hands too often.
The book helped me understand why one straight friend regards me as his best friend, while I do not feel the same way about him. He is drawn to me precisely because I am not a real man. And I am not drawn to him because he is.