I believe that marriage is the most natural state. "And a man shall leave his mother and father and cleave unto his wife." Marriage makes it clear who has sexual rights to whom (staving off murder over women) and provides a very stable home for the raising of children.j
But spouses die and divorces happen. An individual should be complete enough in themselves to live happily without being in a couples relationship should that become necessary.
Basically, being married is not a peace of cake. While it has its joys, it certainly comes with problems. Celibacy also has it's plusses, but it's problems as well. You simply choose which set of plusses/problems you are going to have.
I don't entertain the idea of having sex with others one is not married to: it is irresponsible to one's self, one's future spouse, and to the potential children that come out of such an arrangement (birth control can fail, is is usually not used at all times). I do believe in common law marriages, and think it's stupid that society has gotten rid of them.