Complex sentence: As Loretta and Ronny leave the opera, she sees Cosmo with Mona; both Loretta and Cosmo are shocked to see the other with someone other than their proper partner, but they agree to keep it a secret.
Split into simpler sentences: As Loretta and Ronny leave the opera, she sees Cosmo with Mona. Both Loretta and Cosmo are shocked to see the other with someone other than their proper partner, but they agree to keep it a secret.