Jesus said, “For in the resurrection they neither marry, nor are given in marriage” (Matt 22:30), while Plato said in his Symposium that lovers desired Hephestus to “weld” them together so that “when [they] died, [they] would be one and not two in Hades.”
Such was part of Aristophanes’s myth of the androgyn, that humans had once been androgynous pairs that the gods split into male and female, who now longed for their other half. Such lovers, when they found each other, still yearned to become one again, especially in the next life. Aristophanes then adds the following caveat: “Women who are split from a woman, however, pay no attention at all to men; they are oriented more towards women, and lesbians come from this class. People who are split from a male are male-oriented.”
That is, eternal marriage is a Platonic concept, and Plato had allowances for same gender relationships.
Plato didn’t discuss eternal procreation, but in the Republic he did describe a system radically different than monogamy: shared wives and children. In the Republic, the children belong to everyone, or as Plato says in the Timaeus (which begins by summarizing the Republic), “Everyone of them would believe that they all make up a single family, and that all who fall within their own age bracket are their sisters and brothers, that those who are older, who fall in an earlier bracket are their parents or grandparents, while those who fall in a later one are their children or grandchildren.” Or as Mormon said, “All children are alike unto me” (Moroni 8:17).
I argue here and here that Joseph Smith sought to implement shared marriages as well: or that originally both men and women could have multiple spouses. Such sharing would make allowances for procreation by the larger group that would transcend individuals’ procreative abilities.
 Plato, Symposium, 190-193.
 Plato, Symposium, 191e.
 Plato, Republic, 457c-d.
 Plato, Timaeus, 18d.