Complex sentence: Barber revised the opera, with text revisions by Gian-Carlo Menotti, Barber's long-time partner and librettist of his first opera, "Vanessa" (Heyman 1992a).
Split into simpler sentences: Barber revised the opera, with text revisions by Gian-Carlo Menotti. He was Barber's long-time partner and librettist of his first opera, "Vanessa" (Heyman 1992a).