Thomas Burnham - How many wives? two or three??

Research need : marriage reord for Thomas and an unknown woman between 1796 and 1806
OR
birth records showing a mother for any or all of the group of four above

Let's start with Mary Cowdrey
(1816-1879)
What primary sources are available for her?

in search Is tubled upon Vermont, U.S., Vital Records, 1720-1908 for Thomas Burnham
1870 and Prior
Burnam, R-Burroughs, M
the Marriage of Ruth to THomas which cotradicts the first post above.
They married in Thetford on APRIL 28TH 1810.

I WILL NOW STOP and reorganize the tree

Revision
Established sequence:
1> Thomas marries Mabel and fathers several children with her
2> Mabel left him in 1796 (see) Mabel Burnham (Sexton) timeline
3> A child Betsey is attributed to Thomas in 1806 Betsey Burnham
4> Thomas marries Ruth Ames in August 1810 in Thetford
5> Thomas fathered the remaining children Ruth Ames is the mother of all born after 1810

Whaar seems most likely nowe is that Mable never returned to THomas after she eloped... but we don't know where she went.
The 1806 child Betsey remains a mystery.

Swtitcing to Stillman Burnham (born the year before Thomas married Ruth)
&
Betsey Burnham , likewise , born 1806, 10 years after Mabel left...

My feeling is that a "middle wife" should be creted as a stub.

Here's a hint that there may have only been two wives:
Mary Frances Barbour aka Mary Frances.
If Mabel née Sexton was her maternal grandmother, this same given anme "Mary Frances" might have been passed down from Mabel's mother:
Mary Frances Sexton (1748-1844)
Mary Frances Sexton

The question is: If Mabel made up with Thomas and had more children with him, why did Thomas remarry in 1810?