He used to call me, "Princess", now he calls me, "Kid"

Aren't the words "princess" and "kid" related to each other. For example, if I were to refer to a girl that's a lot younger than I such as a child then I would say either word.

Depends how he said kid, if it's kind of flirty way then he could be just want to change a bit from time to time, saying same word over and over will lose the meaning of the word.

It depends on how he said it. Both could be terms of endearment.