Friends and sex...

Ok... i am sitting here ... and i was looking thru my myspace friends... and thinking about who's had sex with whom...
and amazing... there a few people.. (they aint whores or anything like that) including me... that have slept with their friends and their friends boyfriends/girlfriends...
and its all a secret... only one or two people know that they have slept with this person... who is their best friends man/woman...
It just amazes me and honestly i was the same way... how casual sex has become... just another thing... at one time... it would have been looked down on severly to sleep with your friend's boyfriend or girlfriend even if they werent together at the time... or had split for good. Or if the person you slept with was married, even if they were "sepreated". How people dont think anything bad about sleeping around... friends with benifits... your friends current/ex lover... or a married person...
When did the idea that sex is supposed to be special change?