There's good news for couples reaching the seven-year-itch, as it's not all downhill from here, according to a new study on relationships.Researchers from the Pennsylvania State and Brigham Young universities have found that the happiest point of a marriage is actually when you reach 20 years together.In the study, published in the journal Social Networks and the Life Course, researchers Paul Amato and Spencer James examined data from the "Marital Instability Over the Life Course" study, which included information on the marriages of over 2,000 couples, to identify when happiness rises and declines during a relationship.They found that marital satisfaction gradually declines in the first 20 years, but then stabilizes after this time."Although divorce is common these days, about half of all marriages last a lifetime and the long-term outlook for most of these marriages is upbeat, with happiness and interaction remaining high, and discord declining," the researchers said.The team believes that couples may develop "deeper levels of appreciation" over time, which gives their marital satisfaction a big boost.