Complex sentence: They sing a fond duet, which becomes a quarted as Eliza lists the remarkable catalogue of the food that Thomas has eaten at the refreshment stall, and he explains that he has eaten all of her wares to prove his affection for her.
Split into simpler sentences: They sing a fond duet, which becomes a quartet as Eliza lists the remarkable catalogue of the food that Thomas has just eaten. Thomas explains that he has eaten all of her wares to prove his affection for her.