A love triangle or eternal triangle is a scenario or circumstance, usually depicted as a rivalry, in which two people are pursuing or involved in a romantic relationship with one person, or in which one person in a romantic relationship with someone is simultaneously pursuing or involved in a romantic relationship with someone else. A love triangle typically is not conceived of as a situation in which one person loves a second person, who loves a third person, who loves the first person, or variations thereof.
Love triangles are a common narrative device in theater, literature, and film. Statistics suggest that, in Western society, "Willingly or not, most adults have been involved in a love triangle."
The 1994 book Beliefs, Reasoning, and Decision Making states, "Although the romantic love triangle is formally identical to the friendship triad, as many have noted their actual implications are quite different ... Romantic love is typically viewed as an exclusive relationship, whereas friendship is not."
The term "love triangle" generally connotes an arrangement unsuitable to one or more of the people involved. One person typically ends up feeling betrayed at some point (e.g., "Person A is jealous of Person C who is having a relationship with Person B who, in Person A's eyes, is "their person."). A similar arrangement that is agreed upon by all parties is sometimes called a triad, which is a type of polyamory even though polyamory usually implies sexual relations. Within the context of monogamy, love triangles are inherently unstable, with unrequited love and jealousy as common themes. In most cases, the jealous or rejected first party ends a friendship – and sometimes even starts a fight with – the second party over the third-party love interest. Though rare, love triangles have been known to lead to murder or suicide committed by the actual or perceived rejected lover.
Psychoanalysis has explored "the theme of erotic love triangles and their roots in the Oedipal triangle".