Did your spouse-to-be enter the U.S. with inspection?

Well, first you have to get a marriage license, then get married if that's what you want to do. I presume you are really asking how he gets legalized in the U.S., yes? Well, if he entered the U.S. without documents, or w/false documents, you will file a petition on his behalf, he must return to Mexico, and be interviewed at the U.S. Embassy. If all goes well, he returns to the U.S. and is admitted as a lawful permanent resident. If he entered the U.S. legally, that is, with a valid visa, and I-94 departure card, he is probably likely to be permitted to adjust to green card status here in the U.S. The process is slightly different. Whether or not he has to return to Mexico or not, however, you will have to file a petition on his behalf. So get married, and get that going. Also, make sure you have a good attorney to help you. Good Luck!