He would also need a visa, either a visitors visa or a work visa. Does he have that? If not unfortunately he would not be able to visit you here. My husband has a b2 visitor visa but we never had him come after we started the process altough he could have. My lawyer said that he could visit with no issues up until the case went to NVC and at which point we would need to show proof that he would be returning to his country for the interview and that he still had strong ties, cause it would look like he was just coming here to adjust his status. He could apply for a visitors visa but I know they are hard to obtain. He would never want to mention he has a fiance in the US but he would also not want to lie if he is asked. Best of luck!