Unchained reviews A History Of Mistresses by Elizabeth Abbott, and ends with this conclusion:
What made mistresses tolerable, socially acceptable or even occasionally welcomed in the past were the iron-clad arranged marriages that were completed to join bloodlines, alliances and inheritances — but never love. It was the tyranny and finality of marriage that gave the mistress her acceptable social status.Now, with even England’s royal family divorcing and remarrying for love, the chains of marriage — which Alexandre Dumas once described as being “so heavy that it often takes two people to carry them, and sometimes three” — are palpably lighter.