Adultery is the most difficult to prove of the fault-based grounds. Today, very few divorces are actually granted on adultery because (1) its hard to prove, and (2) the vast majority of cases settle before trial.
But how do you actually go about proving adultery? You've heard that it's difficult, and that the standard of proof is very high, but what does that mean? For practical purposes, what would you have to do? These are all good questions.
First, let's start with the definition of adultery. Adultery is defined in the statute. Adultery is defined as, "[a]ny person, being married, voluntarily having sexual intercourse with any person not his or her spouse."
Adultery is about SEX. By the statute, sex is vaginal, oral, or anal intercourse. That's it. Nothing else matters. Not kissing, not hand-holding, not "I love yous." Adultery is all about the actual physical act of having sex. You'll have to prove that sex either occurred, or that there was such an opportunity for it to occur that there is little doubt in the mind of the judge that it probably did occur.
It's easy to get the divorce filed on adultery, because you just need reasonable belief that the adultery occurred in order to file. You won't have to prove the adultery until the trial. Typically, in a complaint, we'll allege the initials of the paramour, the date the adultery occurred, and the location where we believe it occurred. This will get us in the door.
In order to prove adultery at trial, you must provide strict, satisfactory, and conclusive evidence that adultery occurred, and you must have a witness to corroborate this testimony. In most cases, we use private investigators in adultery cases, because they are the best corroborating witnesses. Of course, this is risky, because private investigators are not very favorably looked upon by judges, but a private investigator is uniquely positioned to get the kind of evidence you'd need to prove adultery.
Sometimes it happens that private investigators get the actual act of sex recorded, but more often we're able to prove that opportunity for adultery occurred. We do this by having the private investigator "stake out" his house, the paramour's house, a hotel, or other location where the two of them are staying. He photographs or videos them going in, watches the exits, makes sure no one leaves during the night, and then (ideally) catches them leaving together again the next morning. This is typically enough proof.
As you can probably guess, it is expensive to hire a private investigator. It's also time consuming. Though adultery does qualify you for an "immediate" divorce in Virginia, there are a lot of steps that go into the process from the moment that the complaint is filed until your final decree of divorce is entered. Usually, before a court will let you schedule a full trial, there are procedural barriers in place–like pre-trial and judicial settlement conferences–all designed to help the parties come to an agreement and settle their own affairs before trial.
Trial is considered a last resort, only reserved for parties who absolutely cannot reach a solution on their own. It's also generally less than desirable, because you're giving all the power to the man in the black robe who, though wise and well-respected, knows the absolute least about the situation of any person in the room.
If the judge isn't convinced by your evidence or your private investigator, you'll have to content yourself with a no fault divorce anyway.