Something deep is being revealed and it might not have anything to do with your fiance, who knows… Grab a pen and start writing out what you feel and think, see it as a chance to grow whatever may happen
I just found out I have a three year old child within me recently, and that was a bit surprising as it behaves like that with tantrums and everything… It just got stuck at that mental age as I repressed it probaly around that young age…