A: Immigration status does not affect whether or not two people can get married. The normal marriage requirements will still apply -- you can't be married to someone else, you have to be old enough to get married, etc. However, if the question you are asking is can the green card holder sponsor the international student for a green card if they get married, the answer is probably yes, depending on their circumstances.
A: When you file to remove conditions on your green card, you will have the opportunity to explain why you are no longer married to the spouse who sponsored you. However, be sure to hire a qualified immigration attorney to help you because this is a complicated legal argument to make.
A: To be eligible for a U-Visa, you must have been the victim of certain types of crimes. These crimes are usually felonies. You also must have been cooperative with the police in investigating and prosecuting the crime. If the facts of your robbery meet these criteria, you may be eligible for a U-Visa. You can find out more information at this website: https://www.uscis.gov/humanitarian/victims-human-trafficking-other-crimes/victims-criminal-activity-u-nonimmigrant-status/victims-criminal-activity-u-nonimmigrant-status, or schedule a consultation with an immigration attorney.