Like most relationships, from torrid affairs to complex love triangles, they can get complicated. And for some couples, they allow their emotions to get the better of them, sometimes even turning to murder. After all, the phrase "crime of passion" was invented for a reason. And whenever you mix sex and true crime, you get a scandalous concoction that's too captivating to look away from. It's no surprise that many famous affair cases have been turned into movies and even TV shows.

"The stories are astonishing," said Susan Lucci, actress and host of Investigation Discovery's Deadly Affairs. "First of all, that so many people over so many years, all over the country, down the street, in the house next door, are choosing not to walk away or [get a] separation or a divorce—that they would actually just murder."

And that feeling of disbelief, of hearing about average people committing atrocious crimes, is what makes it all the more chilling. From people who kill for revenge to those who murder simply to avoid a messy divorce, these affairs started off bad and just got worst. Below, a breakdown of love triangles that ended tragically.