No Going Steady

A semi-aversion of a Love Dodecahedron, only instead of stable, dedicated relationships, the romantic situation is just too scrambled for it to form. Characters seem to go through partners faster than an allergy sufferer goes through tissues. This can land the story more on the cynical side of the Sliding Scale of Idealism Versus Cynicism only if the characters are middle schoolers, where week-long girlfriends and boyfriends happen all the time. With characters any older than that, it usually turns ridiculous.

Compare Dating Do-Si-Do.

Comic Books

 * While it tends to take longer than the above examples, a good chunk of Spider-man's supporting cast has dated other chunks of it. (Flash Thompson has dated TWO of Peter's exes and one girl that had a crush on him, just to pick one example)
 * Archie Comics features a teenage version with nearly every character just casually dating. The girls get mad when Archie dates another, but it's commonly accepted that Archie, Reggie, Betty and Veronica all date whomever they want.

Live-Action TV

 * Degrassi the Next Generation is notorious for characters going through partners as if they were tissues. Some characters went through so many partners that they ran out of people to pair with, and had to date someone they'd been with in previous seasons. In one notable case, two characters changed sexual orientation to be together—and as soon as they broke up, one of them changed orientation right back.
 * 7th Heaven is perhaps the only show more notorious for its musical-chairs dating.
 * In That '70s Show, when Kitty finds out that now Hyde and Jackie are dating, she proclaims "You kids change partners more than square dancers!"
 * The Secret Life of the American Teenager, also by the creator of 7th Heaven, does this a lot. Amy gets pregnant by Ricky then falls in love and illegally marries Ben. Grace dates Jack but then they break up because he slept with Adrian. Adrian dates/sleeps with Ricky a lot but doesn't mind going out with Jack a couple of times. Grace then falls for Ricky who still has sex with Adrian a lot even though he and Grace are technically dating. Ben's best friends, Henry and Alice, were dating but then they had sex too. And apparently it was bad. And the second time was bad too. So they break up and Henry flirts/has a crush on Amy's sister Ashley who also appears to like him. Alice goes out with the then single Jack. But she still is up to sex with Henry...And we're only on episode 14 of season one.
 * The first couple of seasons of Sex and the City ran on this (particularly Samantha), though by the series end they were all in steady relationships.
 * All of which reflected the serious character growth they had undergone during the course of the series, except Carrie's
 * Alex from Wizards of Waverly Place regularly dates and dumps boys. A notable exception was Dean, who she eventually had a real relationship with. They still broke up, though.
 * Both the original and reboot series of Beverly Hills, 90210 were/are known for having the main characters go though partners faster than they change clothes. Kelly is probably the worst offender in the first series and Annie in the sequel.

Video Games

 * Enforced in the original Tokimeki Memorial. Making dates with one girl exclusively is the easiest way to lose. If you don't take other girls you know on dates once in a while, they will feel neglected and "bomb" you, making the feelings of all of the other girls negative - including the girl you're focusing on! The balancing act this creates between building a strong relationship with the character you're truly interested in and keeping all the other girls happy is one of the trickiest aspects of the game.

Real Life

 * Real Life Averts this hard. Whilst they still will get genuine surprise from many, long-standing couples exist that last through High School, or even Beyond, though they are still relatively rare.