Marriage licenses can be declared invalid for a number of reasons. The most common basis for an invalid marriage license is probably fraud, unlawfully procuring a marriage license on behalf of one or both of the parties to the marriage. The parties might enter into a fake or sham marriage, as a means of getting U.S. lawful permanent residence other than a Green Card, or other immigration status. For a marriage to be valid under the law, the spouses have to intend to live in a real marital relationship, namely to establish a life together, following the marriage ceremony, and prove their intention through their actions.
Bigamy, from french bigamie, from Latin bis, twice, and Greek gamos, marriage is a formal entering into of a marriage while a former one remains undissolved. Bigamy is committed when the second marriage ceremony is completed. Only the state in which a second marriage was solemnized will have jurisdiction to charge a person on the offence of bigamy.
Adultery, from Latin adulterium, is the voluntary and consensual intercourse by a married person with someone other than his/her spouse. It is considered objectionable on social, religious, moral, or legal grounds. Adultery is difficult to prove as it requires corroborating evidence from a third party. The law requires that you provide evidence of the adultery from a third-party, such as a private investigator. Direct proof, such as photos, video, recordings, or explicit emails and indirect proof, such hotel or credit card records must be supplied to the court.
Unlawfully procuring a marriage license, bigamy, adultery: defense. N.Y. Pen. Law § 255.20
In any prosecution for unlawfully procuring a marriage license, bigamy, or adultery, it is an affirmative defense that the defendant acted under a reasonable belief that both he and the other person to the marriage or prospective marriage or to the sexual intercourse, as the case may be, were unmarried.