Of course, probably the most important passages
in the bible
are in the first epistle to the Corinthians
In Corinth, as in many other places, some had taken to the practice of celibate marriages. Paul lays down in his epistle that marriage exists as an outlet for sex, and that one should either be celibate and unmarried, or be willing to fullfil the sexual needs of one's spouse. That applies to both of you, by the way.
Other weird practices at the time involved unmarried couples living together chastely. As far as anyone can tell, Paul probably didn't like that. Other things he didn't like seemed to include Simon Peter.
Paul also wrote on marriage in Ephesians. Ephesians is widely considered to contain the pauline domestic code. Notable for not including admonitions to the husband to beat his wife, but rather to love his wife, and treat her as he would his own body.