Fornication: The free act of carnal intercourse between persons who are not married but who are free to marry. Fornication is always gravely wrong because it deprives sexual intercourse of the order which the good of the human race demands. It is a substantial inversion of an essential order.
http://www.catholic-forum.com/saints/ncd03343.htm
Heh.......I use to think the same thing. NO big deal.