SomeGeezer,... think of it this way....
It`s like watching straight porn. Millions of men watch porn.
they see a man and a woman fuck, and even though they see a naked man, they aren`t watching ...HIM. The man being in the porno, doesn`t mean the guy watching is attracted or sexual with other males.
They are focused on the ACT, and the pleasure the WOMAN receives.
Ditto a MMF featuring 2 straight males. They sure aren`t interested in each other. The woman is the focus.
Hope that clarifies.