This is one couple who found great joy in learning to dance that helps them to stay in shape and enjoy their marriage. Carl Boyer and his wife Marge began taking dance lessons 6 years ago when they were retired and just returned from an international dance contest in Canada.
You don't have to wait until retirement: find an activity that you both enjoy and put the fun back in your life again. Not only will it help you stay in shape--when you "play together, you'll stay together."
However, some competitive sports such as tennis can bring out the worst in couples. I've seen near divorces happen right on the court! So if you aren't having fun with one activity, find another that brings out the good side of your better half.