Complex sentence: The next year, while Sylvie is out of the house and Dexter is trying to contain his new wailing daughter Jasmine, unbeknowst to him, Sylvie is actually having an affair with an old friend of his.
Split into simpler sentences: The next year, while Sylvie is out of the house under other pretenses, Dexter is trying to calm his new (wailing) daughter, Jasmine. Unbeknownst to him, Sylvie is actually having an affair with an old friend of his.