marriage

i am having my 2 year fiance comming from nigeria to the states soon and we might get married do we have to go to the courthouse for the marriage license before we marry ?he might have to go back before his visa expires but i do want him to come back .if he goes to embassy what does he need to tell them once he does his visa again.? does he show them he is married and all that ? i want to have a life with him and have 2 kids with him and just be happy...he is the most loving caring man i ever met ..my family loves him and they are happy for us... but i just need to ask u the married question cause i am not sure what we have to do and what he has to do if he goes back before the visa expiration .. we need some options or advise .. he is getting a round trip back but once he goes back what does he need to do so he can come back here again..? i want him in the states to be with me so its not back and forth thing of traveling thanks i hope i hear from u soon