No you just need to be lawfully married for that because that is Constitutional (edit:the right to not testify against your spouse I mean). "Legally" married is for taxes and other statutory benefits and what not...... To lawfully marry you only need a contract between you, the partner and The Creator.....and perhaps a ledger in your family Bible......
....if it ever comes up, when you don't testify against your partner in court you can, in fact, and in good faith, claim your own right, right there on the spot.....because you would not be lying......this is where I would start if I were gay and wanted to marry seriously.......I know it won't help with 401k at the moment (as that is a legal issue not a lawful one)but it is a good solid foundation that isn't too whiny ya know?