The Catholic Church is one component of the polity just as you and I are. It has its influence upon adherents and political bodies. As such, I don't see it changing its view regarding homosexuality anytime soon. I also don't see it supporting legislation that allows for gay marriage.

It's important to understand that church marriage and state marriage are two different things. I'm sure that there are churches that carry out gay marriage ceremonies. But without a state license, such marriages are not recognized as constituting marriage per a state's law or constitution. If it should ever happen that the Catholic Church starts performing gay marriage ceremonies, I'm sure that the state wherein that happens will have already sanctioned gay marriage.