The easiest case I ever had was one where the wife was the one having an affair. Her low life boyfriend took video of them having sex. When she dumped him for someone else, he sent the video to the husband. Having evidence like that is very rare. I had another case where the wife was involved with a woman. She and the lady took still photos of themselves engaging in cunnilingus. In the case of homosexual, extramarital relationships the terms are either sodomy or buggery rather than adultery but the legal consequences in a divorce are the same.
So, if you are not lucky enough to have undeniable photographic or video evidence, how can you prove that the spouse is committing adultery? Back in the 1950′s, before no-fault divorce, proving adultery was necessary much more often than it is today. And the method lawyers used then is still in use today. You hire a private investigator who observes and documents the cheating spouse’s behavior.
The investigator’s observations of the passionate kiss in the parking lot followed by the stroll into the hotel holding hands are circumstantial evidence. Public displays of affection are helpful but not enough by themselves. If the investigator then sees them go up to the room and not come out until the next day, then you have enough to meet the requirement of clear and convincing evidence. One of the things you look for in an investigator is the ability to take photographs or video that can be used in court. If it’s out of focus or too dark or only shows the car, they haven’t really earned their fee.
Often people call and say they have emails or text messages they have somehow captured. That sort of evidence can be helpful but won’t usually be enough by itself. You really have to have someone observe them under circumstances where the only reasonable inference is that they are engaging in sexual activity, specifically oral, genital or anal intercourse. So save that evidence, but just understand you will have to put it together with evidence of them being alone together for some period of time.
The other path is to try to force the paramour to testify. If they are married, they will take the fifth amendment and refuse to answer the questions. But if they aren’t, I have known judges to rule that they have to answer the questions. The paramour’s testimony is going to be sufficient unless there is some strong reason to doubt their honesty.
Sometimes there are friends or relatives of the cheating spouse who are willing to testify about admissions the spouse made to them or behavior they witnessed directly. It is not uncommon for someone close to the cheater to disapprove enough to provide the necessary evidence.