The phrase "everything is fair in love and war" is often attributed to John Lyly, an English writer and playwright who lived during the Elizabethan era. He is best known for his work "Euphues: The Anatomy of Wit," which was published in 1578. In this work, the quote appears as follows:
"the rules of fair play do not apply in love and war."
Over time, the phrase has been paraphrased and popularized in various forms, but the essence remains the same - it suggests that in the pursuit of love or during times of conflict (war), people may resort to tactics and actions that might not be considered "fair" in other contexts.