It is true that the werewolf thing was intended as a metaphor for being gay (or was it aids? One of those, possibly both) in the sense that it was something that got unnecessary prejudice and had therefore to be hidden because it would ruin lupin's career. But that doesn't mean that Sirius had a crush on James. Or that lupin, who married the very female tonks and had a kid with her, was actually supposed to be gay.