Ok. You will need to amend your I-751 and change it to an I-751 waiver.
Here is some information on that:
Focus on where it says, "If You Are In Divorce Proceedings But Are Not Yet Divorced"
Here is a list of things that I like to give my clients and I know that you may not have all of these things, but the more you have, the better it is.
A letter where you describe, in a very detailed fashion, the circumstances in which you met your spouse, the reasons you married, and the feelings and emotions that you had or still have towards your spouse, and why.
If you have a child or children together, the birth certificate for each child.
Wedding pictures and pictures of other moments when you and your spouse, and other members of your families and friends have been together.
Very detailed letters from people who know you and your spouse and who are witnesses that your marriage was valid, who were at your wedding, or who knew you as a married couple.
Love letters or cards that you received from your spouse while in the relationship.
Letters from people addressed to both you and your spouse, or in which the person who wrote the letter refers to both of you as a couple.
Any types of documents that have both your names on them that show that you bought a car, a house, furniture, or anything else together.
Any rental or lease agreements for your home or apartment with both of your names on it or a letter from the building manager or owner proving that you lived together.
Bank or financial statements that show that you had or have a savings or checking account together.
Any insurance documents that show that you were or still are covered by your spouse's insurance plan, or that your plan covers or covered him or her.
Bills, such as electricity, water, heat, cable TV, phone, or others that show both you and your spouse's names.
Jointly-filed Income tax papers (both your names).
An identification card that shows that shows a common address.
Membership cards for video clubs, grocery stores or similar businesses, that show joint membership.
Any other documents that prove your relationship.
You will need to submit evidence similar to the evidence that you submitted at your marriage interview. You must prove that even though you divorced, your marriage was not entered into solely for the purpose of obtaining an immigration benefit.
So you do need to inform USCIS that you are separated and your divorce is in process because you do not want then to approve a regular I-751 as that will cause you a problem when you apply for U.S. Citizenship in the future. So inform them and continue to collect evidence that your relationship was real but just fell apart. It happens and they understand that.
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