From Grammont's footnotes
"Mary, Duchess of Buckingham, was the only daughter of Thomas, Lord Fairfax, and Anne, the daughter of Horace, Lord Vere; a most virtuous and pious lady, in a vicious age and court. If she had any of the vanities, she had certainly none of the vices of it. The duke and she lived lovingly and decently together; she patiently bearing with those faults in him which she could not remedy. . She survived him many years, and died near St. James's, at Westminster, and was buried in the vault of the family of Villiers, in Henry VII.'s chapel, anno 1705, ætat. 66." -- Brian Fairfax's Life of the Duke of Buckingham, 4to. 1758, p. 39. She was married at Nun Appleton, September 6, 1657. In the Memoirs of the English Court, by Madame Dunois, p. 11, it is said, "The Duchess of Buckingham has merit and virtue; she is brown and lean, but had she been the most beautiful and charming of her sex, the being his wife would have been sufficient alone to have inspired him with a dislike. Notwithstanding she knew he was always intriguing, yet she never spoke of it, and had complaisance enough to entertain his mistresses, and even to lodge them in her house; all which she suffered because she loved him." In some manuscript notes in Oldys's copy of Langbaine, by a gentleman still living, we are told that the old Lady Viscountess de Longueville, grandmother to the Earl of Sussex, who died in 1763, aged near 100, used to tell many little anecdotes of Charles II.'s queen, whom she described as a little ungraceful woman, so short-legged, that when she stood upon her feet, you would have thought she was on her knees, and yet so long waisted, that when she sat down she appeared a well-sized woman. She also described the Duchess of Buckingham, to whom she was related, as much such another in person as the queen; a little round crumpled woman, very fond of finery. She remembered paying her a visit when she (the duchess) was in mourning, at which time she found her lying on a sofa, with a kind of loose robe over her, all edged or laced with gold. This circumstance gives credit to Fairfax's observation above, that if she had any of the vanities, she had certainly none of the vices of the court.
http://www.pseudopodium.org/repress/grammont/note… see note 160
Mary, sole daughter and heiress of Thomas, lord Fairfax, and wife of George Villiers, duke of Buckingham, was a woman of little or no beauty, but of great virtue and piety. The duke, who seemed to be all mankind's epitome, well knew how to assume, at least, the character of an affectionate husband; and loved her, very probably in her turn, as she was a complying and contented wife. A man who could equally adapt himself to the presbyterian Fairfax and the irreligious Charles, could, with great ease, become a civil and obliging husband to a woman who was never disposed to check the current of his humour, or correct the eccentricity of his course. She died in 1705, in the 66th year of her age.
---A Biographical History of England. J. Granger, 1775.
Mary Fairfax Villiers, Duchess of Buckingham has her own Wikipedia page.
Of Diary times, it says:
"The couple had no children. The duchess was made a Lady of the Bedchamber to Catherine of Braganza, queen of Charles II of England, and held the position from 1663 until 1692.
"In the course of their marriage, Mary tolerated her husband's mistresses and was called "a most virtuous and pious lady, in a vicious age and Court".
"In 1668, after fatally wounding Francis Talbot, 11th Earl of Shrewsbury, in a duel, Buckingham set up house with his widow, Anna, and Mary Villiers was obliged to return to live with her parents until the liaison ended in 1674."
Chart showing the number of references in each month of the diary’s entries.