Always a composer of intricacy, Mr. Guettel mostly eschews traditional musical-theater forms and simplified melodies; his lyrics here are sometimes conversational, sometimes fragmentary, reflecting the characters’ muddled psyches and their conflicting desires: for the high and the happy blur of booze, but also stable ground upon which their marriage can right itself. Music and lyrics reflect both aspects in the duet “Evanesce,” as Kirsten sings, “I’m leaning out the window, I’m running with a knife,” to which Joe ripostes, “I’m riding on an arrow, I’m running for my life.” Then, together, “I have you now, you are all I need.” In a single song, we see the dynamic that runs throughout the show: abiding love at war with destructive impulses.