Dating a married man memoirs from the other woman
Misteress is defined by Urban Dictionary as "a man other than her husband with whom a married woman has an ongoing sexual relationship".
Until recently, a woman's taking a socially inferior lover was considered much more shocking than the reverse situation.
In its more sinister form, the theme of being "kept" is never far from the surface in novels about women as victims in the 18th century in England, whether in the novels of Eliza Haywood or Samuel Richardson (whose heroines in Pamela and Clarissa are both put in a position of being threatened with sexual degradation and being reduced to the status of a kept object).
With the Romantics of the early 19th century, the subject of "keeping" becomes more problematic, in that a non-marital sexual union can occasionally be celebrated as a woman's free choice and a noble alternative.
Historically the term has denoted a "kept woman", who was maintained in a comfortable (or even lavish) lifestyle by a wealthy man so that she would be available for his sexual pleasure.
Such a woman could move between the roles of a mistress and a courtesan depending on her situation and environment.
"Paramour" is sometimes used, but this term can apply to either partner in an illicit relationship, so it is not exclusively male.