Complex sentence: Simon then receives a call from a distraught Clary who explains that Jace has gone missing and is untraceable and then she explains how much she loves him and that she truly does love him.
Split into simpler sentences: Simon then receives a call from a distraught Clary who explains that Jace has gone missing and is untraceable. THEN she explains how much she loves him and that she truly does love him.