Sans Lawrence, if sodomy is committed in a way where it is illegal in one place and not another, then in the one place if one makes sure the cops watch you do it, you won't get arrested, and in the other place you will, if you can interest them in it all, which typically you can't. So the answer is nothing. Some places a private act is legal, and some places, not.
But gay marriage is a public matter involving the state, as are civil unions, with attendant property rights. A divided House on this matter cannot stand, for long. That is a whole different kettle of fish. Once civil unions get a bit of seasoning, and become fairly common, SCOTUS will indeed weigh in, if Congress does not. It will really have no choice. Under old tools, it would do so on the grounds of the fundamental right to travel, most likely, although the full faith and credit clause is another available tool.
Congress has already weighed in on the gay marriage issue with the Defense of Marriage Act, passed by overwhelming majorities in Congress and signed by Clinton. Of course, after Lawrence, there's a good chance the Supreme Court will strike down the Defense of Marriage Act as unconstitutional.