Often, our romantic entanglements are much more complicated than a simple meet cute, date, marriage, white picket fence, and kids. In real life, people are often dating more than one person at a time, accidently fall in love with someone else, or have open relationships.
In today's prompt, create a love hexagon or some rather random shape by focusing on multiple protaganists.
Write a serious love story about three different people, by overlapping each character's dating patterns and relationships.
You can have a couple as two points of a love triangle (in other words, our main couple is both dating someone else) or you can have three people who are all on the market, dating everyone cute within a fifty mile radius (with some overlapping results, of course).
The goal, though, is to not make judgments on how the characters live their lifes. Americans might have a Puritanical strain in them when it comes to sex and dating and Hollywood might have filled our heads with happily-ever-afters but for this prompt to work, you have to allow your characters to be as real as possible, without imposing harsh critiques along the way. If you do so, you'll alienate your reader by giving away a bias towards your characters.
You can have the bias but you don't want to sound preachy. Instead, show it through the character's end fates.