I have an Irish friend (I'm in the US) who said that a lot of Irish-Americans apparently flew home to cast a "yes" vote on this. Is that true? Is that something that is allowed via Ireland's laws? I know some countries whose people exist largely in diaspora (i.e., Lebanon) have had voting rights extended to such people, at least in certain cases, or extend certain rights to such people (particular involving inheritance and property), but I don't know anything about Irish law.
If it is true, that goes a long way toward answering another poster's question re: "What did you do about it?" If the yes vote can rally people to fly in from outside of the country for their cause, then of course the no vote will lose. It seems like a lot of people who are against this are against it only up to the point when they'd have to stop posting about how terrible it is and actually go outside to do something about it. And, since someone else brought it up, in America such a thing would basically be useless, since such referendums can be determined to be unconstitutional even if voted in by popular vote (e.g., California's Proposition 8, which passed with a 52% yes vote, was overturned on just those grounds shortly afterwards), and this particular right has been invented out of whole cloth by the judiciary in some cases (e.g., New Mexico, which never had a law for it or against it, but which nonetheless decided to force county clerks to issue marriage licenses to gay couples after the state's supreme court found that not doing so was suddenly unconstitutional).
I would be surprised if this "popular vote" approach would be tried here in the USA, since it is obviously not needed. Just keep winning legal victories, and it will become nationwide law in no time, as it probably will be soon. From an efficiency standpoint, it's much easier for the feds to decide this by fiat than to leave things up to state and city ordinances. I'm sure we all remember the recent events in Indiana, and probably recognize that such antagonistic, press-aided conflict is not good for the country overall.
Anyway, congratulations to those who wanted this, and condolences to those who didn't. As usual, the world will continue on either way.