Obama was for it before he was against it. He was for it when he ran for state senate, then against it when he ran for US Senate, then sort for it in 2007, then against it in 2008. Bit the truth is he was always for it.
As for Myth, the man is a chameleon. Dump him in a box of Democrats, he turns blue. Dump him in a box of Republicans he turns red. Just because he was in a blue box first doesn't mean that's what he "really" believes. I don' know if he really believes in anything.
Obama says whatever gets him votes, nothing more, he’s getting on the same-sex marriage issue to hopefully try sex-baiting Romney to argue with him on that issue, whether or not Romney does is entirely up to him. Obama’s desperate, and he is showing it.