I know I said the wrong thing....

My and my bf have been together for almost two months now. We're living together and things are great. Until today... He asked his stepmother to give us a ride to the store today so we could do some grocery shopping. Not a problem. But then he suddenly decides not to go because she's rushing around and he didn't want to go until he ate something. And wanted me to go instead. Now mind you, I went shopping on Sunday and pretty much got everything we need. I told him that I wasn't gonna go either. Then he made a big stink about it but previously I've told him that I don't like depending on other people. There's a bus I could take that'd get me wherever my heart desires. And then I added that I'd rather ask my ex for a ride before I ask his family. I know it hurt him, but I just feel like it's not his family's responsibility to take care of me. If we were an item for a few years, then maybe I'd feel comfortable doing so, but the fact of the matter is that I'm just the girlfriend and they shouldn't have to do anything for me. Am I being unreasonable?