The singer is “holding out for a hero”. There are other men available, but she wants one who has specific traits (strong, fresh from the fight, etc.).
Having another boyfriend/partner would prevent the singer from having the option of partnering with a hero. This is a good example of having an Option Value. Having options has value, and by staying detached the singer leaves open the opportunity for a hero.
Economists mainly have studied option value regarding stock options, but maintaining options has significant value in many areas of life.