I think this may be where the story of the marriage to an Indian originates from:
http://www.batbox.org/Chapter-3.pdf
There's a lot of it, but glancing through there is reference to being an Indian interpreter, selling Indians, and a 10-year-old Indian boy named Thomas Bushby. I saw nothing to suggest that any of the Bushby's returned to England.
The Bushby's in Virginia seem to have obtained land and some status, whereas the children of your George Busby were humble Agricultural Labourers (the marriage licence will probably tell you George's occupation). I therefore suspect that there is no connection between the two families, other than having the same surname. However, if the marriage licence shows George to be a widower then this could be where the story of the death of a wife and child comes from.
So, I've acquired the marriage bond.
I can tell you that it does not indicate whether he is a widower or a bachelor, but it does give three witnesses: John Aspinwall, Sarah Aspinwall and Thomas Jessop. Also, it says they paid £100 for the license, but does not say why.
It appears John was born in 1778 in Chipping Warden, and Sarah was his sister, born in 1777 in Chipping Warden. I can find no other references to a John or Sarah Aspinwall in the area in that time. They are more in Mary Tack's age range, so could have known her, but they were only 17 and 18 at the time of the marriage so could they have been viable witnesses?
The other witness, Thomas Jessop, appears to be Thomas Jessop of Culworth, born on 2 October 1751. He married an Eleanor Gibbs (1756-1835) on 30 March 1779 in Potterspury, and died in February 1839 in Culworth, aged 87 years old. He is roughly in George's age range.
This establishes that George must have been in Culworth for some time before marrying Mary Tack in order to get to know Jessop or the Aspinwalls. But it does not give any indication of where exactly he was between his birth in c1758, and his marriage in 1795. Also, it does not give any indication of parentage. So, the mystery continues.