In order to obtain a K-1 fiancé(e) visa, you and your fiancé(e) must intend to marry each other within 90 days of your fiancé(e) entering the U.S as a K-1 nonimmigrant. Your marriage must be valid, meaning both you and your fiancé(e) have a bona fide intent to establish a life together and the marriage is not for the sole purpose of obtaining an immigration benefit.
If your fiancé(e) marries you within 90 days of being admitted to the United States as a K-1 nonimmigrant, he or she may apply for lawful permanent resident status in the United States (a Green Card).