Austin isn't as much of an island as it may seem. Loads of the smaller towns that fill in between it and the bigger cities have healthy gay populations because of the prevalence of gay-favoured businesses for the tourists and daytrippers. Houston & Dallas both have HUGE gay populations that are very out and very, very, very proud, so they spread the tendrils further.

Sure, there are places where tolerance does not rule (to say the least...hello, Jasper, TX!), but it's easy-peasy to stay on the sunny side. San Antonio isn't any good, as a specific.