I'm thinking of deciding I don't want to move in with my gf and her older sister and child after a month of looking for places
Why don't you want to move in with your gf and her older sister and child?
The child demands a lot of attention and I am not ready to provide it.
It's ok if you don't want to move in with your gf and her sister. You should talk to your gf about it honestly.
I'm not going to talk to her as it's not a big deal.
You should talk to her about it. It is better to come to a mutual understanding and not leave it alone for a month and she is wondering why you have not moved in. Communication is important in a relationship.