According to the research, married couples'
assessment of the quality of their marriage starts
to sink rapidly just after the "I do" and
continues downward through the first four years.
http://www.divorcereform.org/mel/aqualityofmarr.html
According to the National Center for Health
Statistics, the median duration of couples who
divorced between 1989 and 1990 was 7.2 years.
https://www.psychologytoday.com/us/blog/games-primates-play/201202/the-seven-year-itch-theories-marriage-divorce-and-love