The phrase "decrease in marital satisfaction" means that a person's overall happiness and contentment in their marriage has gone down or become less enjoyable. Full definition
Most couples report a 67 % decrease in marital satisfaction after the birth of their children and it doesn't go back up again until after the children leave home. (familyandcouplescounseling.com)
Indeed, the transition to parenthood is associated with a decrease in marital satisfaction (Twenge 2003). (psychologytoday.com)
Know that a decrease in marital satisfaction is normal — and not your or your mate's fault — but that there are many things you can do to increase satisfaction as well (verywellmind.com)