Text underlay issues like that are common in 19th century publishing. English speakers expect syllables to fall directly under the note to which it corresponds. Italians were either sloppy or assumed that everyone would know that seven syllables of poetry would correspond to seven notes.

There’s another giveaway that this song isn’t by Pergolesi. The first line of the song includes an extra syllable not in the original poem. The line should be “Se tu m’ami, sei sospiri”. It’s an ottonario. Someone (Parisotti?) added the world “tu” making it a nine syllable line. That meter is almost never used in Italian poetry and never (at least not that anyone studying this has ever found) in opera libretti. Yes, composers sometimes repeat a line or part of a line, but this kind of alteration, not unheard of in German Lieder, is not typical (I know of no other examples) in Italian text setting, at least in the 17th and 18th centuries. (Things get a little looser starting with Boito.)

I do assign it. It’s a useful song to teach sinalefe (the joining of vowels across words as one syllable in the poetry and on one note of music). If they can do it in this song, hey will have no trouble when this shows up in arias and recitatives.