Not with well over half the states rejecting so-called gay marriage by the vote of the people, I sure don’t see gay marriage becoming the law at all. It’s really more like an extreme minority of states that have gay marriages. New England/New York, Minnesota, Iowa, Washington and forced on California. Not too many.
All states will come to recognize it, just as they all recognize each others marriages now, and the federal employees, the military, and immigrants all can have legal gay marriage as well.
Remember that they don't have to "perform" the marriage, they just can't tell people and parents that they aren't married when they move there, or get transferred there.
States have a long history of regulating marriages, those “cousins marriages” and the like. I don’t think even the Feds can usurp the wishes of those people in places like Arkansas, Oklahoma, Mississippi and impose same-sex marriage on the land. And some places SSM exists was forced on by the court as in Iowa with a few other places done by the legislatures of the state, so I don’t really see it as being popular. It’s been a movement that has used all kinds of tricks and deep pockets as well to force it on the public.