Originally Posted by Marengo
I m not sure if William ever had a mistress actually. I believe there were rumours about Elizabeth Villiers, who was aknowledged as his mistress but the nature of their relationship is unclear. Historians still disagree about William's (supposed) homosexuality though.
In any case, Mary was pregnant but miscarried. After an illness (I do not know which one) she was unable to have children anymore.
In my personal opinion, I'd say that sex did enter into the relationship, but I doubt that the affair was as notorious as most historians make it out to be. William was so discreet about this liaison that no one knows when he even saw Elizabeth. I read that he was ashamed of his errors and this could explain not only his discretion, but also the fact that until he decided to bestow upon Mistress Villiers confiscated Irish estates belonging to James II, he never so much as furnished apartments for her, which was the usual treatment. Elizabeth was a force in politics, and a great conversationalist, but since William's interest in sex was far from being strong, it's doubtful their meetings were always of a romantic nature.