Corbis Images

Like any Valentine's Day, not everyone has a special someone and there are a lot of lonely hearts out there feeling a little left out.

Weathering the day can be difficult for singles. But as dim as a lonely life can look, love can be downright dark at times. In this slideshow, explore some of the most insane couples in history.

SEE ALSO: Animal Pairs Prove Love Is Blind

Corbis Images

Donatien Alphonse François, Marquis de Sade, the man whose name and reputation brought us the term "sadism," is not someone whom you would expect to be much for marriage. But the Marquis was married and did claim to love his wife, Renee-Pelagie de Sade, and she in turn was devoted to him.

Unfortunately, Marquis de Sade was not one for monogamy, and regularly engaged in licentious activities without his wife knowing, even conniving with his mother-in-law to keep her unaware. His wife eventually became not just aware of her husband's lascivious activities, but also an enabler of them, which included orgies with young women and even an affair with her sister.

The Marquis' lifestyle and writings frequently caught up with him, however, and he spent his life in and out of prison. By 1790, his wife had had enough and divorced him.

WATCH: Your Brain in Love

Corbis Images

The love Queen Victoria and Prince Albert of Saxe-Coburg and Gotha shared is legendary. As close to love-at-first-sight as any romantic relationship, the two were seemingly inseparable during their 17 years together, which resulted in nine children.

After Albert's untimely death in 1861 at age 42, Victoria became overwhelmed with grief, embracing widowhood as no other person in history. She secluded herself from the public and donned black for the rest of her life, a full four decades after Albert's passing.

SEE ALSO: Brain Takes Less Than Second to Fall in Love

Just because Albert was dead, however, didn't mean that Victoria thought he was out of touch. According to a book published last year, Victoria held séances after Albert's death in which she attempted to communicate with her late husband.

John Brown, with whom Victoria shared a close, though platonic, relationship for 30 years, would be the queen's medium when she wanted to speak with Albert, and she reportedly kept detailed notes of their discussions. After Brown's death, Victoria wanted to publish her notes, only to be dissuaded by her private secretary, who threatened to resign, fearing a scandal.

Wikimedia Commons

If case there was any doubt that love could triumph even over death, look no further than the case of Carl Tanzler, a man who's Valentine's Day is a lot more like everyone else's Halloween, except darker.

While working as a radiology tech at Marine Hospital in Key West, Tanzler met Elena Milagro de Hoyos, a patient suffering from tuberculosis, a disease that, though treatable today, was fatal in the early 1930s. De Hoyos, a local beauty, captured Tanzler's heart, and he was determined to see her through her illness.

SEE ALSO: Secret and Sordid Sex Lives of Scientists

Under the care of Tanzler, who was a technician, not a doctor, de Hoyos underwent a number of treatments, none of which proved at all effective. During that time, Tanzler demonstrated his affections with gifts to de Hoyos. But all the unrequited love and untrained medical treatment couldn't save de Hoyos and, unsurprisingly, she died.

At his insistence, Tanzler paid for her funeral and mausoleum, which he would visit nightly for two years. That is, until he had the bright idea of bringing de Hoyos' decomposing corpse home with him. Tanzler used wax, wigs and plaster of paris to gussy up the body, replacing skin, bone and even an eye. Tanzler kept it in his home for seven years, until de Hoyos' family caught wind of what he was up to and reclaimed her remains.

Federal Bureau of Investigation

Bonnie Elizabeth Parker and Clyde Chestnut Barrow were a pair of American outlaws who seemed to have as much a passion for the fast life as they did for one another.

During the early years of the Great Depression, the two were part of a larger gang that robbed small banks and gas stations in the South and Midwest, murdering at least 13 people along the way. Hardly as successful as their notoriety suggested or as glamorous as was later portrayed by Hollywood, Bonnie and Clyde lived a desperate lifestyle evading the law and scraping a living together with small scores.

In 1934, the duo was ambushed by lawmen in Bienville Parish, La., after being betrayed by a friend. They died in a hail of gunfire, succumbing to dozens of bullet wounds.

SEE ALSO: What Bonnie and Clyde Left Behind

Corbis Images

Before there were Craigslist personal ads -- and couples luring unsuspecting people through those ads in order to murder them -- there were lonely hearts ads, which were the fashion for crazed couples looking for deadly thrills.

Couple Raymond Fernandez and Martha Beck set the standard in the late 1940s when they murdered upwards of 20 women by luring them in through lonely hearts ads. Even a child fell victim to their violent streak. Fernandez would draw in the women and the duo would then spring their trap. If Fernandez showed any interest in the potential victim, however, Beck would get violently jealous with both her victim and her accomplice.

The pair was arrested in 1949 and each executed by the electric chair two years later. Each professed their love for the other in their last words.

SEE ALSO: Most Wanted Women: FBI's Female Felons: Photos

Corbis Images

While the United States had the Lonely Hearts Killers, on the other side of the pond, the United Kingdom had the Moors murderers, another couple who famously came together as serial killers.

From 1963 to 1965, Ian Brady and Myra Hindley committed a series of murders, with four children and a teenager as their victims. The duo buried their victims at Saddleworh Moor and even took photos of themselves smiling at the burial site. All but one of the victims, Keith Bennett, were discovered by police, who had the assistance of the killers in tracking the remains down.

Both Brady and Hindley spent the rest of their lives incarcerated. Hindley died in prison in 2002, and Brady, diagnosed as criminally insane in 1985, is still alive today.

SEE ALSO: Personal Manifestos: Never a Good Sign

Corbis Images

Anybody who thinks money can't buy love -- or at least an approximation of it -- never got the opportunity to meet Anna Nicole Smith and J. Howard Marshall.

The courtship began as would any typical paid relationship between an older man and a young woman: While performing at a strip club in Houston, Smith became acquainted with Marshall, an octogenarian who made his fortune in oil, in 1991. The two were married three years later, in 1994.

Marshall died more than a year after the marriage, setting off years of legal challenges over the late tycoon's $1.6-billion estate. Nicole Smith, who became very famous for the relationship, herself died in 2007 of a drug overdose.

SEE ALSO: Celebrity Deaths: Homicidal and Accidental

Nikolas Schmid-Pfähler and Carolin Liebl via

Want to see what the future of love looks like? Look no further than Vincent and Emily, a robot couple programmed to have something of a love-hate relationship.

As Discovery News' Alyssa Danigelis reported last year: "Each spindly robot is mounted on a box and contains motors, gears and sensors that allow it to move around at human-height. Their "heads" regard each other with various expressions."

The pair interact by sending either positive signals, such as moving up close, and negative signals, such as moving away. This video shows how a typical "dialogue" between the two typically goes.

The interactions between the two might not seem as meaningful to outside observers, but then again, the robots would probably be perplexed by our species ritual of giving dying plants, chalk candy, bad poetry and skunky water as tokens of affection. In fact, out of all of the couples on this list, they seem the most normal of the bunch.