Isabel Leonard as Mexican painter Frida Kahlo and Carlos Álvarez as her husband and fellow artist Diego Rivera perform in a scene from Gabriela Lena Frank's El Último Sueño de Frida y Diego at New York's Metropolitan Opera. Marty Sohl/Met Opera hide caption toggle caption Marty Sohl/Met Opera Frida Kahlo and Diego Rivera have inspired books, films and plays with their evocative paintings and passionate, turbulent relationship. Now, the 20th century Mexican painters are protagonists in an opera. "We all see elements of this relationship in our own relationships and how we replicate these kinds of toxic elements too," composer Gabriela Lena Frank said ahead of the May 14 opening night at New York's Metropolitan Opera .…