Complex sentence: He met the family in Mannheim in 1777, and fell for Aloisia, who was pursuing a singing career; when the Webers moved to Munich, where Aloisia had an engagement, they ran into Mozart again.
Split into simpler sentences: He met the family in Mannheim in 1777, and fell for Aloysia. When the Webers moved to Munich, where Aloysia had an engagement, they ran into Mozart again.