@TheArtfulDodger,
Well, as far as I can tell (and I can't quite tell), that's pretty central to what you're asking about gay marriage (aka 'marriage'.)
Part 1: Same-sex marriages are made legal, (at the state level, federal level, or both). This is all that the government can do.
Part 2: Some churches agree to conduct same-sex religious ceremonies. Some don't.
The ones who don't will likely get pushback, and things will go from there. That's not a legal/governmental issue though, it's an internal church issue.