For the most part, gay marriage is currently not legal in our country, though there are a few places is it. I predict that it WILL be legal in all 50 states within the next 20 years, and that happens one of two ways.
A: Public opinion: Those opposed tend to skew older, those in favor tend to skew younger. As the older ones die off and are replaced by younger folks who have an opposite opinion, a critical mass will eventually be reached.
B: Constitutional Process. This has begun, with the Prop-8 ruling. If that ruling is upheld by SCOTUS, it’s game over, gay marriage is instantly recognized as a constitutional right in the entire country. I believe SCOTUS SHOULD rule that way, but I acknowledge that it’s an open question, and we won’t know until it happens.
The first relies on public opinion, in the second public opinion is irrelevant, unless it’s widespread enough that it can support a constitutional change.