Hacker's may have the temptation to blackmail you, a private investigator would keep things confidential and legal so you would have nothing to worry about when they are done with their investigation. So if you are wrong you are out the cost of the private investigator to do their investigation and that is it.

If a private investigator does find something then you have all legal documents to use, with a hacker you would have nothing that you could legally use if you chose to get a divorce because you obtained evidence illegally. Then your husband would have a legal standing to divorce you and get the bulk of what ever you two had together after getting married. Which would grant him with the ability to sue you afterwords in criminal and civil court using the evidence you obtained illegally against you.

It is a loose loose situation for you if you obtain what you want to know illegally. You can only find out what you are wanting to know illegally by getting a private investigator to legally obtain what you asking for. When they are done they will normally present you with their findings with high quality images, videos and other documents that you can have when the investigation is done to do with as you want.

In short, a hacker is illegal to use and a private investigator is the route you should take to keep things private so no one knows what is going on but you and the private investigator.