Love and statistics

In a previous Seville bloggers meet, Zifra and Luis taught me The Prisoner's Dilemma. In the most recent one, Zifra made me think again about human relations in challenging ways. 

When a couple hugged I said that the more happy couples are there in the world, the more statistically probable it is that single people will end up in a happy couple themselves. Zifra, who happens to be a Math professor, said I was wrong: the more couples there are, the less chances single people have of ending up in a couple because there are less singles available. Who is right?

Both of us are because we were talking about different things. Zifra referred to available, single people: evidently, in a world with plenty of singles it is easier to find a partner. But I was not talking about simply pairing up: I believed that every happy couple is a small piece of evidence of the existence of love. The more loving couples there are, the likeliest it is that true love exists. Zifra never said a word about love, though...