Complex sentence: She became the mistress of Robert Bignell, the proprietor of the Argyll Rooms and together they visited Paris, a place she fell in love with so much that she refused to return to London with Bignell.
Split into simpler sentences: She became the mistress of Robert Bignell, the proprietor of the Argyll Rooms. Together they visited Paris, a place she fell in love with so much that she refused to return to London with Bignell.