Opera’s grim fascination with ‘fallen women’ — as Welsh National Opera has called its latest mini-season — lies largely in the spectacle of the fall itself. But in Hans Werner Henze’s Boulevard Solitude, the composer’s 1952 operatic debut, the heroine — a tart denied even a heart — starts off near the bottom; her fall is less precipitous than those in the other two operas the company has chosen for its theme, Puccini’s Manon Lescaut and Verdi’s La traviata.