Your ex-spouse doesn’t need to wait for 2-years period to be over and can file for I-751 Waiver immediately after the divorce is finalized.
After he/she will file for this form, he/she will be called for an private USCIS interview with an investigator, where he/she will have a burden to prove that the marriage has been bona fide (entered in a good faith, not for the purpose of getting a green card).
There are no rules how to prove it and there is no list of evidence to support your facts. Each case is different and unique.
Green Card Marriage Fraud: Fight Back! 
i am also experiencing a living hell with this person i married from Peru and he has made my life in little peaces but as soon we married he has had a his other women already with children and recently had another but my problem is that he has meet other women whom works in a domestic program that he has been having sexually relationships and she has been helping him committed this marriage fraud so as soon as he left without me knowing in what he was doing just one day he got mad and next day i was served with restrain order against me but it has been 12 months and i moved to Idaho where i got a chance to file a restrain order on him then he turned around and filed one against me but i filed first he has raped and beat and done so much more that i haven’t reported due to the other women that is helping me in org eon i went to Idaho for help they said i couldn’t do it in Idaho cause the crime was committed in org eon but he has done everything he could to falsely accuse me of false accusations and has left me homeless has token my cars has gotten my electric turned and him going by my house laughing with his other girlfriend he has had all this time that now he uses to do his work i tried to file a restraining order against her to but was denied i feel i cant defend my self but i dont want him to get away he is a child abuser predator on older women and takes all they have and pretends to be a victim
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