Um romance que explora o que é "humano", através de um casamento humano / humanóide. Provavelmente antes do 1964

Que poder be Os amantes por Philip Jose Farmer, publicado pela primeira vez na 1952. Eu não li, mas o prazo está correto, o resumo da trama abaixo parece plausível, e não havia muitos autores de SF abordando esse tipo de assunto nos 1950s.

Escaping the religious tyranny of a 31st-century Earth by a fluke assignment to the planet Ozagen, linguist Hal Yarrow found that the worst of Earth had followed him - Pornsen, his personal Guardian Angel, vigilant for any evidence of sin or wrong thinking. Conditioned by a lifetime of submission, Yarrow would have accepted Pornsen's constant spying as an unpleasant necessity and lost himself in the study of the language of Ozagen's intelligent dominant race, the Wogglebugs... but then, hidden in ancient ruins built by humanoids long vanished from the planet, he found Jeanette, a not-quite-human fugitive. For a Believer like Yarrow, unconsecrated contact with any female was forbidden - and love for an alien was unthinkable. But to Yarrow, in every way that counted, Jeanette was warmly and bountifully human. So Yarrow sought the aid of the amiably tolerant Wogglebugs to keep his harboring of Jeanette a secret - and at the same time concealed from his alien allies Earth's farreaching plans for them and their unexploited planet. Yet there was one secret Yarrow did not know and could not imagine... the very special nature and needs of the woman he loved!