Brad Davis plays the title character with all the emotion of a dead fish. Yet Davis plays Querelle as if he were completely disinterested in anything happening around him. All the other characters in this film follow Davis' lead and become as stiff as cardboard. Of course, Fassbinder's script gives them no indication of what the hell this film is about anyway, so instead of playing their characters as ambiguous or shadowy, the principles here simply move as directed and mouth their lines dispassionately. Murder here is committed for no reason and without motivation.
Sex is committed with the same indifference.
He is not alone, in fact, all but one of the male characters here engage in gay sex. But no one in this film has sex that isn't coupled with violence, anger and deceit. He realizes that he can be butt-fucked without any emotional involvement but to fuck someone else he must become passionate. It is all the same. For example, Querelle and his brother Robert may be the same man.