Our own place

My fiancé and I live with his mom. He says he doesn't want to move because she recently got divorced and I understand that, but I recently found out that I'm pregnant and that house is sooooo small. There is going to be no room for a baby and we have the money to move even if it's an apartment. His mom doesn't like me all the time. It's sort of like she's nice to my face, but when I'm in the other room, she always seems to find something to complain about. Am I being stupid for being upset that he doesn't want to get our own place?