I would build on that by reiterating that there's a dramatic disjunct between the people of Texas and the politicians of Texas at the moment. Gay marriage is one of the issues that illustrates it well.
Consider that in 2005, Texans amended the state constitution to clarify that marriage is only between a man and a woman; 76% of voters were in favor of that. (As it stands, thirty other states have amended their constitutions to ban gay marriage.) Clearly, then, Texans were hugely against gay marriage. But we have to say were rather than are because marriage equality is a relatively new issue, and one where views around the country are changing quickly. In 2005, according to Pew, 53% of Americans were against gay marriage, and 36% were in favor. Today, 48% of Americans support gay marriage, and 43% are opposed. Texas is changing too, albeit from a different starting position. Here's how Ross Ramsey, in October, summarized the latest University of Texas/Texas Tribune poll:
Voters here remain open to some form of legal partnership for gay and lesbian couples, with 36 percent saying they would allow those couples to marry and another 33 percent saying they would allow civil unions but not marriage. Another 25 percent said those couples should have neither the right to marry nor form civil unions. Read one way, 69 percent would allow some form of legal partnership; read another, 58 percent are against same-sex marriage in Texas.
That's a change, even if Texans still lag the nation as a whole. (And you have to wonder what the numbers would look like if people weren't given the option of civil unions, or if Texas had seen any local advocacy for gay marriage during the intervening years.)
If you were just polling elected officeholders, however, I bet you could easily find a 75% majority against gay marriage, and probably against civil unions for that matter. The usual reasons apply: years of Republican hegemony and Democratic torpor have created a situation in which the Republican primary is, in many cases, more important than the general election. The political battles are therefore being fought between the right and the far right. And both camps have reason to oppose gay marriage. The latter because they're against it, and the former because--even if they're not philosophically opposed to gay rights-- public displays of moderation, or even disinterest, bring them nothing but trouble.
Consider some of Texas's wayward Republicans: In 2011 Rick Perry said he was fine with New York's new gay marriage law, and within days he was scrambling to clarify that he meant he was fine with states having their own laws, not gay marriage, of course. Joe Straus once voted against a bill that would have banned gay couples from becoming foster parents, and every two years since then conservatives have tried to oust him as the Speaker of the House of Representatives, partly because of it. In October John Carona, a state senator from Dallas, said that although he wasn't in favor of gay marriage, he had been wrestling with the question--that is, he publicly acknowledged an alternative perspective on a measure he opposes--and he's even had to backtrack from that.
All of that being the case, it's extremely unlikely that Texas would authorize gay marriage of its own volition before the federal government somehow forces its hand. As Ramsey said, you can read the UT/TT poll as showing that a majority of Texans oppose gay marriage. But even if you read them the other way, and conclude that a majority of Texans support some form of equality for gay couples, that's not enough, at this point, to override the Republicans' tactical advantages--the number of offices held, the way the district lines are drawn, vast fundraising capacity, and of course the constitutional ban that's already in place.
At the same time, if the Supreme Court does somehow force the issue of marriage equality, my sense is that a majority of Texans would be sanguine or at least resigned to gay marriage at this point. (I support gay marriage.) I would also guess that a Democratic statewide candidate who supported gay marriage wouldn't be sunk by that issue alone. Texas's relatively moderate Republicans might not even be wholly opposed to an outside assist; some of them are quietly grousing about the far right's stranglehold on state politics. So a Supreme Court ruling in favor of gay marriage could illustrate how isolated Texas is from the national mainstream, as Burka says, but a furious backlash to such a ruling could also illustrate how isolated some of Texas's leaders are from their general electorate.
With regard to gay marriage in particular, incidentally, the Texas Republicans who seem squishy on their opposition tend to cite a suspicion of government meddling. That was a motif in the Carona and Straus examples and it might be a fruitful line of argument for marriage equality advocates, especially in the vaguely libertarian West.