I found a Robert Durham in Spotsylvania Co. VA in 1733 married to Agnes. Is this your ancestor?
3 Oct. 1733 Robert Durham £200 as administrator Nicholas Nicholas, Deceased.
6 Aug.1734 Robert DurhamFredericksville, in the Parish of St. George, d. 15 Apr. 1734.Wit. Charles Barrett, Adam Gordon, William Wombwell Cliff. Ex. Charles Chiswell, Gentl. Leg. wife Agnes; daughters Hannah and Ann, which I had by the said Agnes.
2 Oct. 1734 marriage of John Jones and Agnes Durham."