There is no amendment or any paragraph about marriage in the Constitution. It is silent on the issue and per the 10th Amendment, left to the States.
BUT the 2nd A is pretty clearly part of the Constitution.
As to your life partner choice, I don't give a rat's backside. Whatever.
But if you fail to support the Second Amendment it is much more likely that you'll find yourself being hunted by the government should it ever swing back towards the "Theocracy" side from the "Communist" side.
The 2nd A cuts both ways. It is our last check to keep the government from an extreme form. EITHER side of the pendulum.
Even Kos gets it:http://m.dailykos.com/story/2010/07/04/881431/-Why-liberals-should-love-the-Second-Amendment