Eternal triangle
An eternal triangle (aka love triangle) was a situation in which one person is loved by two others, or one person who loves another is loved by a third person.
In 2269, Leonard McCoy described the complicated relationship between android Rayna Kapec, mortal Human James T. Kirk, and the formerly immortal Human Flint as truly being an eternal triangle, given Flint's longevity. (TOS: "Requiem for Methuselah")