You can only report, the government will decide whether to come back to you.
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Sorry, it is too late to withdraw the I-130 ... it is also too late to withdraw the I-864.
Meet with an immigration lawyer to learn of your long-range obligations.
Unfortunately, CIS/ICE receive literally 'tons' of 'bad marriage' letters ... they rarely investigate, unless it is part of an organized marriage fraud ring. Sorry.
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You have done your part by letting the Department know your thoughts. Since you are divorced, your spouse will file the I-751 seeking waiver of joint filing. Depends on the paperwork he presents to show the bona fides, the Department may/ may not take your letter seriously as in most divorce cases, parties are bitter and USCIS get these letters all the time.
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