In New York, adultery is one of the grounds for divorce, meaning you can file for divorce if your spouse has engaged in an extramarital affair. To use adultery as a basis, you must provide evidence of the affair, such as witness testimony or correspondence. However, New York also allows for "no-fault" divorces, where you can file based on an irretrievable breakdown of the marriage. A divorce lawyer can help you understand the implications of choosing adultery as your grounds for divorce.