I'm straight, so it doesn't affect me.
I live in the UK, so it REALLY doesn't affect me.
The UK already legalised gay marriage a couple years back, so it won't affect the country in which I live.
Basically it doesn't affect me beyond making me really happy for the LGBT community in the States.
But who knows. It could turn me and every other heterosexual male in the universe gay, open the gates of Hell, heralding the fiery procession of the Dark Prince come to steal all of creation from the powerless corpse of God while faithful blood is spilled in sacrifice to the New Master and their bodies sullied and devoured by the faithless and the demons who now rule the crumbled husk of the mankind's former glory. It's 50/50 really.