Ok. You should start the divorce process now and gather as much evidence that you can that she only married you for a green card. The evidence has to be good because there are two very harsh penalties for marriage fraud:
The first, 18 U.S.C. § 1325(c), provides a penalty of up to five years imprisonment and up to $250,000 fine for any "individual who knowingly enters into a marriage for the purpose of evading any provision of the immigration laws."
The second is a permanent deportation from the U.S. This means that she can never immigrate, even if she marries a different U.S. Citizen and even if she has U.S. Citizen children.
You can report marriage fraud in three different ways:
1) You can go to http://www.ice.gov/webform/hsi-tip-form and file the report there.
2) You can call the ICE hotline at 1-(866)(###) ###-####
3) You can contact the local USCIS field office by going to http://www.uscis.gov/about-us/find-uscis-office/field-offices
You should have evidence of the marriage fraud handy in case they want to ask you questions or have you send evidence to them.
As to what that evidence could be, it could be anything that you think of. Witness statements, letters, emails, recordings, etc. The more you have, the better it is.
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