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Use "unfaithfully" in a sentence
"Both have made damning accusations of the other side for negotiating unfaithfully, publicly and informally."
"But Catherine suspects her husband of infidelity, and so makes the unusual move of hiring a prostitute, the eponymous Chloe Amanda Seyfried to attempt to seduce David and see if he reacts unfaithfully."
"Thirdly, the danger of being unfaithfully counselled, and more for the good of them that counsel, than of him that is counselled."