financial problems with fiancé

We've been living with his parents for 2 years and have a son together he's 2 months..we're low on money and can't afford babysitter so I stay home to raise our son.. we're both 19. I want to move out with him but he pays his mom his whole check to pay her rent and buy her whatever she needs, she does not work and had 5 other kids to take care of but doesn't so he has to provide for them as well. I had a talk with him about saving his money but he never has any to save and said what would you do if you were in my position? I don't know what to do we're supposed to get married but I'm holding off until we get our own place i just don't know what to do and how to get him from giving his mom all his money..she needs to get a job and raise her own kids their all in school