my interpretation of it is that if your in a relationship u see loads of hot girls and u wanna be single, but if ur single u miss havin a girlfriend... hence, no matter what side your on the grass always looks greener on the other side..... did u ever stand in a field and look over into the distance and see a field that looks so much greener than the one your in (in reality its not) ? thats where the saying came from !!