400 a month is heck of a deal...there is no way you can..compete with that...i gurantee it will cost you more than that if u venture out on your own and u surely will end up in one of those categories mentioned above..lol...now jokes apart..u will have a secure and safe future  with your brother...dont think about moving until your brother says something that hurts your feelings or treats u bad..but be real myann...its very hard to find people who are willing to help you out. he is not asking you much because you are new (i can make out that you are pretty new in america from the way you are talking) he must have had hard time in his initial days and he is just helping you adjust....its hard to find people like that...as time passes by ask him how can you help him?? its not going to stay 400 forever..mind that..and about the favor thing ...ill say you are lucky..so dont move out yet..