Summary from Wikipedia

Scandalously and unconventionally for the era, she lived with the married George Henry Lewes as his conjugal partner, from 1854 to 1878, and called him her husband. He remained married to his wife Agnes Jervis[7] and supported their children, even after Jervis left him to live with another man and have children with him. In May 1880, eighteen months after Lewes's death, George Eliot married her long-time friend, John Cross, a man much younger than she was, and she changed her name to Mary Ann Cross.