I agree with lomrie089, excpet i've always thought it was about someone that had been raped, and has moved on and is trying to have a relationship with someone new. But she feels like she has to tell him first. And she thinks about the kids she could have someday and how happy she could be. And (like imaginexothat said) that if she told this new person about her rain, or bad times, he could be her hero.
I agree with lomrie089, excpet i've always thought it was about someone that had been raped, and has moved on and is trying to have a relationship with someone new. But she feels like she has to tell him first. And she thinks about the kids she could have someday and how happy she could be. And (like imaginexothat said) that if she told this new person about her rain, or bad times, he could be her hero.