Matthew 19:5 . . . For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh? (6) So they are no longer two, but one. Therefore what God has joined together, let man not separate.
[I believe this last statement means "what God declares or regards as being joined together . . .," not necessarily a union that took place in holy submission to his will. Verse 5 suggests that God's plan was for sex to occur only after the deliberate and public act of leaving one's parental authority for the purpose of joining oneself to other.]