"It is not your love that sustains the marriage, but from now on, the marriage that sustains your love."

Those words of wisdom were written by Dietrich Bonhoeffer in a letter to his best friend, who was soon to be married, from the Gestapo prison he was held in during the last years of his life.  The idea that marriage sustains love, and not the other way around is one that our culture today need so desperately to understand.  Far too many marriages end when the two people in it don't feel like they're "in love" anymore; the emotions that brought them together have lapsed or faded (as most honest people who have been married a long time will tell you they at times do), and therefore the rational for the marriage itself is gone.
From God's perspective, the value of the sacrament (to borrow a word from our Catholic friends) of marriage is that it sustains us as a union of two of God's children through good times and bad.  It is not dependent upon what is felt but rather rests upon the promise and commitment that has been made before God and man. 
What is it that brings a marriage through a rough patch or dark days and back again into the light and joy of love?  The very commitment that is needed from both man and woman to stay with this union regardless.  It is when we honor each other by remaining true to our word that we allow God carry us through the circumstances that may destroy a marriage not founded upon trust in God, so that we can rediscover what made love bloom in the first place.
When a marriage breaks up over the ebb and flow of life a profound opportunity for growth and character has been forever lost.  It is for our own benefit that we should remain and strive for our marriages.  Our culture would like people to think that they deserve to find happiness and therefore should leave when a marriage isn't "happy", but that lie is selling something is cannot deliver.  Where is happiness without someone to share it with?  Where is happiness in selfish decision making?
It is when two become one, till death, that love can truly be that which sustains us.