Your divorce must be finalized before you file for a K-1 fiancé visa.
This is required by United States Citizenship and Immigration Services (USCIS).
If you are in the process of finalizing your divorce when you submit your I-129F application, USCIS may deny your petition.
The K-1 fiancé visa allows your fiancé to come to the United States in order to prepare for your wedding.
However, USCIS only grants these visas to individuals that are serious about getting married.
For this reason, they require that you prove to them that you are legally eligible to marry. You are not legally eligible to marry your fiancé if you are already married to someone else.
You may ask yourself what is the big deal if you are in the process of finalizing your divorce when you submit your I-129F application.
Keep in mind that one of the biggest goals of USCIS is to detect and eliminate marriage fraud.
Marriage fraud is a fake marriage that takes place for the sole purpose of obtaining permanent residence in the U.S. A fiancé visa applicant that is already married may indicate fraud to USCIS.
Additionally, you must marry your fiancé within 90 days after your fiancé arrives in the U.S. Divorce proceedings usually take months, if not longer, and could cause you to miss this deadline.
This is the last thing you want to do since USCIS is looking to see if you are serious about getting married when they process your application.