Forever love?

Marriage. Does it promise forever love? In an ideal world, we would all hope so. But the reality is far from it. About two years ago, I was talking to a co-worker about family and marriage. Her parents had divorced after being together for nearly 15 years. They were college sweethearts and had a very loving relationship. But why the divorce? She said that they merely fell out of love. A few years later, they both remarried other people and stayed the best of friends. How, in an ideal world, does this work? More importantly, why do people fall out love?
Is it lack of communication? Does the passion just die out? Infidelity? Domestic abuse? Financial stress? Or for no particular reason at all? The reasons could be endless.
Despite popular belief, statistics show that the divorce rate in the USA has decreased (3.7 in 2006, 3.5 in 2008) (See www.cdc.gov). At the same time, marriage rates have also decreased although there has been an increase in the country's population . More people are choosing to stay single or opt for live-in relationships. Even in a country like India, more women are getting married after their late twenties, if they marry at all. Commonly asked questions now are: what are the benefits of marriage? am I too independent to get married? will I be less happy if I choose to remain single? Is marriage the goal of life? If you stand strong long enough, family and societal pressure tends to wear off. They figure you to be a lost cause and move right along with their lives. In the future, country consensus reports have to provide for information on the number of single citizens in a country, the number of couples living together, the number married, and the number divorced. Mere analysis of the married or the divorced will fail to suffice. I guess this is bound to make life and the world more interesting.
All this said... do such radical changes in the world and in societies across the world bear witness to the truth that we are starting to become more tolerant and more understanding of individualism? And if we, as human beings, are learning to appreciate individuality and the freedom to choose and live on individual terms, is it so unfathomable that two individualistic and tolerant people can make a marriage work AND remain in love at the same time?
Finally... Keeping in the mind that not all marriages have 'The Notebook' ending, is it unrealistic, nonetheless, to strive for such a passion and satisfaction in marriage? Maybe we could learn a thing or two from Nicholas Sparks's books, for somehow they just seem to make love simple and love in marriage even simpler...