The first time the theme appears in this piece is in the recit. Variations on the theme appear for the first time in measure 14 when the vocal line in the aria begins. This is especially clear in m. 17-18 when the material greatly resembles m. 4-5. Another variation on the theme begins at measure 35. The melody is very different, but the same basic dotted rhythm is there, as well as similiar harmonic material.
This piece is based off of a bass ostinato. The ostinatio part appears first in the 4 measure intro to the aria. The aria seems to have two different sections. The A section is the "when I am laid" section, and the B section is the "remember me" section. The A section consists of two phrases. There is a HC in measure 17 and a PAC in measure 32. The B section has two phrases that are repeated twice. I would call the form of the aria simple binary, because the A section never returns.