Complex sentence: Berlioz discovered her at the Odéon Theatre performing the roles of Juliet Capulet and Ophelia and immediately fell in love with her and sent her letters despite never having met her.
Split into simpler sentences: Berlioz discovered her at the Odéon Theatre performing the roles of Juliet Capulet and Ophelia and immediately fell in love with her. He persistently sent her letters despite never having met her.