So what is that wedding garment? This is the wedding garment: "But the goal of the commandment," says the apostle, "is love from a pure heart, and from a good conscience and from an unfeigned faith." That is the wedding garment. Not any sort of love; even people after all, who are companions in a bad conscience are often enough seen to love each other. Those who commit armed robberies together, who engage together in witchcraft, who share their devotion to play-actors, who yell encouragement to their favorite charioteers and huntsmen, they all, very often, love each other. But you don't find in them "love from a pure heart, and from a good conscience and from an unfeigned faith." It's only such love that is the wedding garment.
-Saint Augustine (concerning Matthew 22:1-10)
Alright, lets put this in 21st century English. Love from a pure heart is the only kind of "true love". Yes, lots of people are able to love. I'm not saying that they don't love each other. But the only true love comes from those who have a pure heart.
"In so many millennia, the humans never did figure love out. How much is physical, how much in the mind? How much accident and how much fate? Why did perfect matches crumble and impossible couples thrive? I don't know the answers any better than they did. Love simply is where it is." (from the book 'The Host')