Ephesians 5 says marriage is a model of Christ and the church. In marriage, two very different (almost opposite, although certainly complementary) people form a single unit, just as Christ and the church are united although they are so different in nature. Whether we appreciate the symbolism or not, it is inherent in every marriage between a man and a woman.
Homosexual marriage and adultery are perversions because they mock this Christ/church model.
Man/woman couples can still honor this highest purpose of marriage, to model Christ and the church, even if they don't have children, love, or financial security.
Excellent exigesis! And it's the one model that doesn't have any exceptions.