I think you're exactly right, ASUADPi.
I would guess that most classics scholars would consider it anachronistic at best to apply a gay/straight/bisexual or homosexual/heterosexual analysis to Alexander and Hephaestion because that would be applying a modern understanding instead of a contemporary (as in contemporary to Alexander) understanding.
Here's a good, and not too long, article on the subject:
Was He Really Alexander's Lover....?