From the New York Times blog by Jane E. Brody's "That Loving Feeling Takes a Lot of Work":
"Studies by Richard E. Lucas and colleagues at Michigan State University have shown that the happiness boost that occurs with marriage lasts only about two years, after which people revert to their former levels of happiness — or unhappiness."
Relationships take care, tending, attention...like all living things! Relating to other persons and behaving in the fashion you would like to be shared in reverse makes for a more pleasant life, yes :)
(BELOW) Stevie Wonder's "Overjoyed", live at London's O2 Arena: