The letters reveal how Einstein lost most of his Nobel Prize money in bad bond investments on Wall Street, and provide details of how he was showered with affection and gifts by his many mistresses...Link (via 3 Quarks Daily)
He became involved with Elsa, a cousin, in 1912 when he was still married to his first wife Mileva, a fellow scientist with whom he had two boys, Hans Albert and Eduard. Before he and Mileva married, they had a daughter, Lieserl, who was given up for adoption.
In 1919, Einstein divorced Mileva and married Elsa, but within four years he was in love with Bette Neumann, his secretary who was also the young niece of one of his friends. Many more liaisons followed.
The letters reveal that a beautiful Berlin socialite named Ethel Michanowski followed him to Oxford, only to discover that he was involved with a third woman.