Love and sex are heavily satirized in The Beggar's Opera. Walpole was still well known for having a long suffering wife and a mistress who he kept in town. Those of us who shake our heads in wonderment at the adulterous shenanigans of politicians and the aristocracy will find much to recognize in this opera. The hilarious results of the Highwayman MacHeath's inability to ration himself to one woman at a time are immediately familiar to the modern audience. Marriage is seen as an encumbrance - husbands and wives are there to provide a comfortable living and then got rid of.
Money is the standard for measuring love.
Sex in The Beggar's Opera is merely a business, as in the hilarious and reviling idea that there exists in this society a man whose job it is to get arrested prostitutes pregnant, so they may escape execution or transportation. Ultimately, Gay's message is twofold. Alas, nothing seems to have changed since 1728.