Not all cultures have religion, but they all have marriage, and it always involves a man and a woman. For instance, even with polygyny and (much rarer) polyandry, the plural wives aren't married to each other, nor are plural husbands married to each other. It's always the male-female bond that consttutes marriage. Isn't that so?
I leave this exerpt from that monumental work:
50. How grievously all these err and how shamelessly they leave the ways of honesty is already evident from what we have set forth here regarding the origin and nature of wedlock, its purposes and the good inherent in it. The evil of this teaching is plainly seen from the consequences which its advocates deduce from it, namely, that the laws, institutions and customs by which wedlock is governed, since they take their origin solely from the will of man, are subject entirely to him, hence can and must be founded, changed and abrogated according to human caprice and the shifting circumstances of human affairs; that the generative power which is grounded in nature itself is more sacred and has wider range than matrimony — hence it may be exercised both outside as well as within the confines of wedlock, and though the purpose of matrimony be set aside, as though to suggest that the license of a base fornicating woman should enjoy the same rights as the chaste motherhood of a lawfully wedded wife.
51. Armed with these principles, some men go so far as to concoct new species of unions, suited, as they say, to the present temper of men and the times, which various new forms of matrimony they presume to label “temporary,” “experimental,” and “companionate.” These offer all the indulgence of matrimony and its rights without, however, the indissoluble bond, and without offspring, unless later the parties alter their cohabitation into a matrimony in the full sense of the law.
52. Indeed there are some who desire and insist that these practices be legitimatized by the law or, at least, excused by their general acceptance among the people. They do not seem even to suspect that these proposals partake of nothing of the modern “culture” in which they glory so much, but are simply hateful abominations which beyond all question reduce our truly cultured nations to the barbarous standards of savage peoples.
For a link, I give that to all who want to be educated: