I’m also interested in the modern suggestion that you can have a combination of love and sex in a marriage - which no previous society has ever believed.

De Botton is pointing to what he sees as a historically unusual expectation placed on modern marriage: that one partner should simultaneously satisfy romantic love (emotional intimacy, admiration, companionship) and sexual desire over the long term. He suggests that earlier societies tended to distribute these needs across different institutions or relationships—marriage as economic alliance, kinship duty, or childrearing arrangement, with passion imagined as separate or transient. The quote critiques the modern ideal for being both alluring and potentially destabilizing: by making marriage the sole container for love and sex, it raises the bar for “success” and can turn ordinary fluctuations in desire or affection into a sense of failure.