Only U.S. Citizens can sponsor their fiancés. In order for a U.S. citizen to sponsor his or her fiancé, one must show that he or she is free to marry (i.e. he or she is not currently married to someone else); that they have a bona fide relationship with the fiancé and that he or she and the fiancé have met in person within the two years immediately prior to filing the petition with the U.S. Citizenship and immigration service.
If the fiancé visa petition is granted, the fiancé will not enter the United States with a green card. Instead, the fiancé will have 90 days from the date of entry into the United States to get married to the petitioning U.S. Citizen. Once the U.S. Citizen and the fiancé are married, the U.S. Citizen will then file a petition with the U.S. Citizenship and Immigration Service to obtain a green card. The fiancé can only obtain his or her green card through the U.S. Citizen petitioner.