One possibility is that, due to the length and nature of your relationship in Texas, the clerk is of the opinion that you had a valid common law marriage with this person such that, even though you don't have a marriage license (not required for common law marriages) to properly end that relationship you need to file for divorce.
Another possibility is that the person is looking at a chart that says "When a person comes in asking for X, they must provide Y", and can't get past the fact that for your request "Y" is defined as "divorce papers and/or marriage certificate".
But we're stuck guessing.
Is the issue here that you want to get the Texas license in the name listed on your birth certificate, but they won't accept that as evidence of your name given that all of your other ID reflects the alternative surname you've used for the past fifty years? Or is the issue that they will only use the name from your birth certificate even though you want them to use the name from all of your other ID? Or is it that, due to the discrepancy in names, they won't issue a license at all?

