If you fall in love with someone who lacks the legal right to live in the United States, things will be more challenging than usual if you reach the point where you want to marry.
The U.S. government makes fiancé(e) visas available for this purpose, however getting one is never a foregone conclusion and will require considerable paperwork. The official term for this visa is a K-1 visa.
Sponsoring your fiancé(e)
If you wish to apply for a K-1 Visa for your future spouse you must be a U.S. citizen. Holding a green card is not enough, so if you have one of those you need to try and get your citizenship first. You will need to show you have the financial means to support them although once you marry they can also work.
Proving your relationship is genuine
You’ve probably heard of scam marriages, where a U.S. citizen marries someone they are not in love with to help them get a green card. The government wants to avoid these, so it expects all applicants to prove their relationship is genuine.
Find as much evidence as you can that shows your relationship is genuine. If you lived together in another country, rental contracts or bills in your joint names could help. Copies of emails or messages between you and photos and videos of your time together can also play a vital role in showing your relationship is genuine.
90 days to marry
If you succeed with the application you only have 90 days to complete the marriage once the other person lands in the U.S. Consider booking a slot at the registry office well ahead of time.
Even if your relationship is genuine, you could see your application rejected due to paperwork errors or insufficient proof you meet all the requirements. With appropriate legal guidance, you can reduce the chance this happens.