It could happen.
The first round of the French Presidential election is to be held on Sunday, with the runoff on May 6th. Every poll shows that the two most popular candidates by far are the current President, Nicolas Sarkozy, and the French Socialist Party's candidate, Francois Hollande.
And every poll taken in 2012 that pits the two of them alone against each other has Hollande winning by at least six percentage points, with the latest poll I can google up showing Hollande with a 10% lead.
Hollande and the Socialist Party are in favor of same-sex marriage
Beyond economic policies that are central to this election, Hollande's agenda is modern centre-left: he would permit gay marriage ((and)) legalise adoption for same-sex couples...while Sarkozy is not, and has recently reaffirmed that position.
French President Nicolas Sarkozy on Tuesday said that if reelected he would not support reform of a partnership law to allow gay marriage...
"For me, a family is a father and a mother, not two fathers or two mothers," Sarkozy said.
The Presidential election having been decided, elections for France's National Assembly (the lower legislative body, France also has a Senate) will take place a month later on June 10th and June 17th. It is customary but not guaranteed that the people provide the President they just elected with a governing majority in the National Assembly. Assuming this to be the case, and given that the Senate is already in the hands of the Socialists, should Hollande in fact win the path would be clear for his government to enact marriage equality.
I have no idea how long it would take for such a law to be passed and then come into effect (the United Kingdom's ruling Conservative Party claims it will take until 2015 to get a similar law enacted and into effect there, despite support from the opposition party). Or even whether the Socialists, once in power, would make it a priority. Certainly the French public supports same-sex marriage. The latest poll listed in Wikipedia, from almost a year ago, shows 63% in favor of same-sex marriage, and polls as far back as 2008 record similar statistics.
Whether it takes a few months or a few years, it seems that before long the entirety of Western Europe -- save Italy, and perhaps Switzerland and Germany -- will have marriage equality. Portugal, Spain, Iceland, Norway, Sweden, Belgium and the Netherlands have it. Denmark has enacted such a law; it will go into effect in June. Finland is still considering it, and in Ireland popular support is very strong, with possibly as much as 70% of the population support.
It's time to start pressuring Andorra.