Am I so out of date?

I love tv shows like Friends but I'm intrigued if human nature has radically changed since I was 20 something. Is there a new kind of person who can know their mate has slept with many others and not be bothered by it just a little? These characters on sit coms dance in and out of serious relationships apparently with no one having residual jealousy or rage and want to kill the previous lover. Is this a fact of free love or is the network trying to keep fresh plot lines? Admittedly, when the star gets into a final relationship the series is going to die.