Should I leave or not?

Part of me wants to move out from my bfs/ his moms house but I’d feel bad because I want to leave for selfish reasons and not anything my bf did. The problem is 1.) we don’t have money to go anywhere unless I moved back home and 2.) my bf won’t move to my hometown. The reason I want to leave is because I’m pretty much forced to watch his niece pretty often. His sister won’t step up as a parent so his mom is taking care of the niece. But his mom also works and when neither his mom, his sister or daycare can take her I have to watch her, which is pretty much every weekend and whenever she is sick which happens quite often. I have my own son to take care of and can’t/ don’t know how to take care of a 4 year old. She also doesn’t listen to me very well and my bf always seems too busy to help. I don’t know what to do……