Being faithful to his wives – and 10 girlfriends – was a matter of relativity for Albert Einstein, new documents show.

Einstein freely discussed his affairs – and complained of being chased by the love-crazed women – in letters to his second wife, who was also his cousin, and even to his stepdaughter.

“It is true that M. followed me and her chasing after me is getting out of control,” the world-famous physicist wrote to stepdaughter Margot in 1931. “I will tell her that she should vanish immediately.”

He was talking about a beautiful socialite, Ethel Michanowski, who had left Berlin to pursue Einstein in England – until she found out he was cheating on her with another girlfriend.

Einstein had at least 10 lovers in addition to the two women he married after affairs with them, Barbara Wolff, archivist of the Einstein letters at Jerusalem’s Hebrew University, said yesterday when the letters were unveiled.

He talked about several of the paramours in the letters, including a “Mrs. L” who was another wealthy German, Margarette Lenbach.

Other lovers were identified only as Estella, Ethel, two Tonis, Betty and Margarita, his “Russian spy lover.”

“Out of all the dames, I am in fact attached only to Mrs. L., who is absolutely harmless and decent,” he wrote to Margot.

“I don’t care what people are saying about me, but for mother and Mrs. M it is better that not every Tom, Dick and Harry gossip about it.”

The author of the Theory of Relativity donated his personal papers to the university before he died in 1955. Margot gave it another 1,300 of his letters, with the stipulation that they couldn’t be made public until 20 years after her death, which came July 8, 1986.

The letters opened yesterday also revealed that Einstein lost most of his 1921 Nobel Prize winnings in the stock market and was a much better father than previously thought.

But it was Einstein’s love life that got the most attention. He seemed to live up to one of his famous quotes – “Gravitation is not responsible for people falling in love” – with almost constant womanizing.

During his bitter first marriage to mathematician Mileva Maric, they were often apart. Einstein cheated on her by conducting a long affair with his first cousin, Elsa.

Maric bore him two sons during the 16-year marriage. Soon after they divorced in 1919 he married Elsa and then cheated on her with his secretary, Betty Neumann.

In the letters, he asked Elsa’s daughter, Margot, to help him with another girlfriend. He requested that she pass on “a little letter for Margarita, to avoid providing curious eyes with tidbits.”

The various girlfriends shared some of Einstein’s interests and went sailing or attended concerts with him, the university archivist said at a press conference yesterday.

His relationship with Elsa was a “marriage of convenience,” according to Hanoch Gutfreund, chairman of the university’s Albert Einstein Worldwide Exhibition.

But he wrote to her almost every day and revealed his doubts about his work.

“Soon I’ll be fed up with the [theory of] relativity,” Einstein wrote to her in a postcard in 1921. “Even such a thing fades away when one is too involved with it.”

With Post Wire Services