In this data set, the average married person is indeed happier than the average never married person. But people who are only "pretty happy" with their marriage are actually a smidge less happy overall than the never married, and people who are "not too happy" with their marriage are even more miserable than people experiencing a separation. The numbers, from most happy to least happy ("very happy"= 1, "pretty happy=2," and "not too happy"=3 - i.e., lower numbers mean more happiness):
Average Overall Happiness
very happily married
pretty happily married
not too happily married
Bottom line: Unless you are "very happily married," you are happier if you don't get married at all. Fortunately, almost two-thirds of married people affirm that their marriage is very happy.
Needless to say, there are dozens of obvious concerns with these simple comparisons. But the exercise is still worth doing - and the simple results are consistent with common sense.