What proof do I need to file for divorce on grounds of adultery?

Short answer

You need clear, lawfully obtained evidence, such as a confession, a private investigator's report, or documented communications, showing your spouse had voluntary sexual intercourse with another person of opposite gender. You must also file within 6 months of discovering the adultery, and you cannot continue living with your spouse for more than six months after discovery if you intend to rely on this fact, as courts apply both time limits strictly.