Possible Clues:

• Bedcover very defective - two share it
• Irving Berlin's 'You're Just in Love,' e.g.
• It may call for four hands
• Collaborative work
• Donizetti's 'Tornami a dir che m'ami,' e.g.
• Musical piece by two performers
• 'You Don't Bring Me Flowers,' e.g.
• 'Up Where We Belong,' for one
• Puccini's 'Flower ___'
• Work for two performers