What was Washington's relationship with Sally Fairfax as noted in the biography, Washington: A Life?

Sally Fairfax was the young, beautiful wife of Washington's friend, George William Fairfax. For many years during Sally's marriage to George William and before Washington's marriage to Martha, the two appear to have developed a strong friendship. Washington and Sally often exchanged letters. These letters occasionally mentioned conversations that imply a certain intimacy between the two. Later, in the months before Washington was to marry Martha, he wrote a letter to Sally that goes further in suggesting something of a love affair between the two. However, it is unclear if the affair was ever consummated or not. After his marriage to Martha, Sally and George William remained close friends of the couple, often going to Mount Vernon to socialize. This implies that there was nothing consummated in Washington's relationship with Sally.