Complex sentence: Toby has become wary of Todd, and when he returns he tells Lovett of his distrust, unaware of her complicity in his crimes, he promises to protect Mrs. Lovett, whom he has come to love as a surrogate mother.
Split into simpler sentences: Toby has become wary of Todd, and when he returns he tells Lovett of his distrust, unaware of her complicity in his crimes. He promises to protect Mrs. Lovett, whom he has come to love as a surrogate mother.