A love triangle is a romantic relationship involving three people. While it can refer to two people independently romantically linked with a third, it usually implies that each of the three people has some kind of relationship to the other two. The relationships can be friendships, romantic, familial (often siblings), or even pre-existing hatred between rivals. A combination of straight, bisexual, and gay characters can add significant possible combinations of sexes, and of romantic and sexual interactions.
The term "love triangle" almost always implies that the arrangement is unsuitable to one or more of the people involved. One person usually ends up feeling betrayed at some point. A similar arrangement that is agreed upon by all parties is sometimes called a triad, a type of polyamory, although polyamory usually implies sexual relations. Within the context of monogamy, love triangles are inherently unstable. Unrequited love and jealousy are common themes in love triangles. Though rare, love triangles have been known to lead to murder or suicide committed by the actual or perceived rejected lover.
In television shows, a love triangle is often prolonged, delaying final declarations of love between the pursued character and suitors that may prematurely end this dynamic or displease fans. Similarly, romance films also sustain this set-up until near the film's end, although they tend to establish a more clear-cut conclusion to the romantic entanglements than in long-running TV shows.
A common love triangle is one in which the hero or heroine is torn between two suitors of radically contrasting personalities; one of a girl next door or nice guy type, and the other as a physically attractive but potentially hazardous person. Alternatively, the hero or heroine has a choice between a seemingly perfect lover and an imperfect but endearing person. In this case, the "too-good-to-be-true" person is often revealed to have a significant flaw, such as hidden insensitivity or lecherousness, causing the other person to become the more desirable partner.
Love triangles can either be relatively balanced, in which the two candidates each have a fair chance of ending up with the protagonist, or they can be lopsided, in which the hero or heroine has an obvious romantic interest in one of the candidates, and considers the other candidate as "just a friend," but withholds a confession to avoid hurting feelings. But in this latter case, to provide necessary tension and drama, the second platonic candidate is also very often the hero or heroine's long-term boyfriend or girlfriend.
A less permanent love triangle occurs when a former lover of the main character makes an unexpected appearance to win back the character's heart, provoking feelings of jealousy from the main character's steady partner. However, this situation is usually not considered an actual love triangle since there is little possibility of the main character breaking up with a longtime partner to pursue a just-introduced character, and it is often used as only a test of the true depth of the main character's devotion to their partner. In these cases, the long-term partner has usually been guilty of neglect toward the main character and in the end, the relationship remains intact with the long-term partner having learned some valuable lesson.
Usually, a love triangle will end with the hero or heroine confiding their feelings in the suitor they feel is most virtuous or has the most interest in them. The other suitor usually steps aside to allow the couple to be happy, or comes to terms with their feelings, often claiming they couldn't love the main character as much. Sometimes they are written out of the love equation entirely by falling in love with someone else, or being killed off or otherwise eliminated. While love triangles can be accused of being clichéd, if done well, they provide insight into the complexity of love and what is best to pursue in a romantic relationship.
A love triangle should not be confused with a ménage à trois, a three-way relationship in which all members are romantically involved with each other instead of being in conflict over one person.
Love rectangle is a somewhat facetious term to describe a romantic relationship that involves four people, analogous to the typically three-sided love triangle. Many people use this term for a romantic relationship between two people that is complicated by the romantic attentions of two other people, but it is more frequently reserved for relationships where there are more connections. Minimally, both male characters usually have some current or past association with both female characters. These relationships need not be sexual; they can be friendships or familial relations. Both males and/or both females can also be friends, family members (frequently siblings) or sworn enemies.
An example of a love rectangle in classic literature is in William Shakespeare's A Midsummer Night's Dream, between the characters Lysander, Demetrius, Helena, and Hermia. Demetrius is granted Hermia's hand in marriage by her father, but Hermia loves Lysander, and the two flee, intending to elope. Demetrius pursues the couple, and Helena pursues Demetrius, whom she has always loved. The fairy Puck, in trying to use magic to resolve the situation, temporarily transfers both men's affections to Helena. Further tampering restores Lysander's love for Hermia. Demetrius, now in love with Helena, withdraws his claim on Hermia, and both couples are wed.
Another love rectangle happens in Mozart's Così Fan Tutte, where female characters Dorabella and Flordiligli (siblings) are Ferrando and Gugliemo's girlfriends respectively, and by the end of the opera they "accidentally" swap their boyfriends.
The love rectangle concept is popular in television programs such as Lost (Jack/Kate/Sawyer/Juliet), That '70s Show (Kelso/Jackie/Hyde/Laurie) and One Tree Hill (Lucas/Peyton/Nathan/Brooke). Also within the Harry Potter movies(Harry/Ron/Hermione/Ginny).
For additional terms, the word "love" can be added to the front of other shapes to reflect romantic relationships involving more people, e.g. "love pentagon" or a "love hexagon."