I've been married 3 times. First time at 16, divorced 4 years later. He was 27 to my 16 years.
Second time lasted 21 years. I left when I couldn't stand the control issues he had anymore.
Third time's a charm. William and I have been married 12 years, and are still madly in love. When we got married, a good friend that had at the time been married for 30 years told us, "Find SOMETHING to laugh about EVERY day, no matter what life brings...seek out something that will make you both smile"
The other thing I always remember is a couple that had been married for 78 years were interviewed. When asked their secret for staying happily married that long, she responded, "We never fell out of love with each other AT THE SAME TIME."
I really do believe that a couple, individually, will fall in and out of love several times in the course of their union. The key is to "tough it out" until you fall back in love... :)