One of the wackier aspects of the anti-gay-marriage amendment--because 1) lawyers are a perverse and twisting breed, and 2) the amendment was written as stupidly as possible so that it couldn't be discomprehended, it could be argued that it invalidates all marriages.
http://www.savetexasmarriage.com/
has more details, but it boils down to "Let Marriage = X, but all cases of X are invalid." Now, the spirit of the law assumes that Marriage is the only valid case of X, but it would require only minimal stress to the law to create a bad technicality for some, oh, say, commonlaw couple.
Aaanyway...please vote! And please encourage other people to vote :)
Best,
Jacob