Byron writes:

Mariana has made a conquest of Dervise Tahiri, Viscille [,]Fletcher and Sullee my new Tartar have each a mistress, "Vive l'Amour!"

Letter to J.C. Hobhouse from Athens, 23 August 1810.

Byron writes the words in quotation marks. If this is what I think it is, then it is the earliest reference so far to the song!