The terribly near-incestuous habit or tendency of a tight-knit group of mixed gender friends to date and sleep with one another at various turns in different permutations over a given span of time, often from high school and well into their early adulthood years. Extra messed up if there are siblings in this circle.
This is most prevalent with individuals who are unwilling or unable to make expansions to their social circles due to geographic constraints or cultural isolation (e.g. Orange Country, California) or psychological hesitance to escape the known and the familiar.
Only known remedy to this provincialism is to transplant oneself to New York, London or any other major metropolitan meat market.
Susan left Howard for Dave after they broke up, but Howard picked up Ana when she piqued his interest after she and Jason started agreeing to see other people. Both Dave and Jason are now competing for their long time friend Christie's attention, who in turn as been looking to rekindle passions with ex-boyfriend Howard. Howard and Dave are both secretly cheating on their current girl friends with Christie's slightly older sister, Clare, who has just recently entered this Circle of Friends
They're all going to the same college together next fall.