If you are the fiancé of a U.S. lawful permanent resident (someone who is not a citizen, but holds a green card) and you currently live outside the U.S., your options for gaining U.S. entry and joining your fiancé are limited. That is true whether you want to stay in the U.S. for a short time or permanently.
There are no fiancé visas available for foreign nationals wishing to marry U.S. permanent residents. Fiancé visas are available only to people coming to the U.S. to marry U.S. citizens.
Don’t lose hope, however. There are ways to get yourself into the U.S. if you are the fiancé of a permanent resident, although they may take a long time. The main ways are:
• Marry your fiancé first, then begin the entry process as a spouse of a permanent resident. This method involves your U.S. spouse submitting a visa petition to U.S. Citizenship and Immigration Services (USCIS) on Form I-130, with documents including a copy of your marriage certificate; then you waiting (currently about a year and a half) for a visa to become available in this category (during which time you have no right to live in the United States). If your spouse becomes a citizen during this time, you automatically become an "immediate relative," and can apply for your immigrant visa/green card right away.
• Wait until your fiancé becomes a U.S. citizen, and begin your entry process as a fiancé of a citizen. This method involves your U.S. spouse submitting a visa petition to U.S. Citizenship and Immigration Services (USCIS) on Form I-129F, then you applying for a K-1 fiancé visa and entering the U.S., then getting married within 90 days and applying for adjustment of status (a green card).
• Come to the U.S. on a tourist visa and get married here (with the idea of returning home afterward). This is legal, but risky—the officials at the U.S. border may not believe that you truly plan to leave after the wedding, and may refuse you entry.
Each of these options obviously has advantages as well as drawbacks. And as you can see, the quicker your U.S. fiancé or spouse becomes a citizen, the quicker you can enter the United States. A permanent resident can apply for U.S. citizenship five years after getting a green card (with some exceptions allowing for an earlier submission of the N-400 application).
Talk to an immigration attorney for a full analysis of your options.