Daniel Erickson, lead writer of SWTOR, wrote:
For the last thousand years the Sith Empire has needed stability and growth more than anything else. That means alliances that prevent power struggles. It means encouraging the creation of more children. Which in turn means marriage and a focus on family.
Where once the individual was judged largely alone, bloodlines are now incredibly socially important. A Sith from a long line of powerful Sith will find his path through the Academy easier, his opportunities increased. A family with no Force-users who suddenly find themselves with a Force-sensitive child will sacrifice everything they have to get them martial training and mental discipline coaches – for if that child passes the Academy and becomes Sith the entire family will rocket to the penultimate social class in Imperial society, side by side with moffs and governors, second only to Sith themselves.
Marriage among the Sith is usually between only two people and is often to forge a political alliance. Marriages of love do happen often among the lower ranked Sith but decrease the closer the Lord is to the top of the pyramid-shaped power structure. Marriages between Sith and non-Sith are rare as the Sith believe it dilutes the chance of a Force-sensitive offspring. It is a common, though unspoken of practice, for Sith parents to kill a non Force-sensitive offspring and deny it ever existed, claiming the baby was stillborn, etc. A Sith with openly non Force-sensitive offspring is believed to be admitting the thinness of the blood in his or her family line.
Adultery is common among the Sith but officially illegal. Divorce is strongly frowned upon but killing one’s spouse for adultery or any other provable offense is socially acceptable. The one time you see obligatory divorce is when a member of the Dark Council breaks a couple apart to stop the assimilation of too much power in one place.
This is very interesting. It kinda resembles a lot of ancient imperial societies.