Kevin Federline is revealing how he learned Britney Spears dumped him for good! As we previously reported, the former dancer wrote in his upcoming book, You Thought You Knew, that they broke up in 2006 after he walked in on the pop star "snorting a fat line of coke" at the release party for his album Playing With Fire - when she was still breastfeeding their two children, Sean Preston and Jayden James. As the National Library of Medicine states, you should wait to breastfeed at least 24 hours after cocaine use to ensure the drug is out of your system.