Adultery was a crime in New York at the time of the NDA. Which means it's not a legal contract, as it's purpose was to cover up a crime.
A contract or contractual provision in violation of the law is void from the beginning, it cannot be enforced in court.
If testimony is otherwise admissible and not privileged, it would be a violation of the law for you not to testify. So even if your NDA included a clause saying that you will not testify in civil or criminal court about the subject matter of this agreement, that would be void, unenforceable, and ineffective. The reason for this is completely obvious.