If it's in his name only, you will have no legal right to the home. You can enter into an agreement with him under which he will repay you the money if you cease living there and/or when the home is sold, but if he violates the agreement, all you could do is sue him personally--i.e. such an agreement does not give you any legally enforceable right to the home. Only being on the title gives you a legally enforceable right to the home. You may wish to not do this, but rather wait until the two of you can qualify for a mortgage that would allow you to be on the title.