It is important that you follow the U.S. immigration law once you enter the United States as a K-1 fiancé(e). One of the requirements for a K-1 visa is that you and your fiancé(e) must intend to marry within 90 days of your fiancé(e) entering the United States. So, if you entered the United States as a K-1 fiancé(e), but for whatever reasons, you did not marry the United States citizen who petitioned for you, that means that you are violating the U.S. immigration law. Your fiancé(e) status automatically expires after 90 days. The fiancé(e) status cannot be extended. Even if you marry a different United States citizen, you will not be able to get a green card without leaving the United States first. Your K-1 status only allows you to receive a green card if you marry the specific United States citizen who petitioned for you.
So what can you, as the fiancé(e), do? According to USCIS, you should leave the United States before the end of the 90-day period, if you do not marry. If you do not leave the United States, you would violate the U.S. immigration law. As a result, you can be removed or deported from the United States. That could affect your future eligibility to receive United States immigration benefits. To avoid being removed or deported by the immigration officials, you must leave the United States immediately.
Besides leaving the United States if the marriage does not take place, the only other option you may have is to apply for asylum. You may be eligible for asylum, if you cannot go back to your home country, because you are afraid of being harmed there for the reasons of your race, religion, nationality, membership in a particular social group, or political opinion. You should consult with an experienced attorney to discuss whether you are eligible for asylum. For more information, please see our related article, Asylum.