It simply means he loves you, no matter what he calls you .
What does it mean when someone that is very special to you ,you both have very strong feelings for each other and he calls you princess on somedays and on somedays call you by your first name?
It is just his mood
It means on some days he sees you as a Princess, either from royalty standpoint or needing to be rescued in a tower...depends on his point of view, and other days he "sees you" like in Avatar.