The situation sounds like a film noir plot device. A suspicious spouse looks up a private detective in the yellow pages and proceeds to hire them to keep tabs on their husband or wife to see if they are being unfaithful. In a perfect world, this would only happen in black and white movies. Unfortunately, it actually takes place all the time. A Houston private investigator recently interviewed by Channel 26 Fox News says that in the vast majority of cases he confirms the spouse's suspicions.
There are many reasons why a couple may decide that their marriage is no longer working. Infidelity is obviously one of the most painful symptoms of marital problems. In many cases though, saying that the infidelity ended the marriage is putting the cart before the horse. Often, it is simply the instance which negates any excuses and makes both partners come to terms with the fact that the marriage has fundamental problems, that must either be resolved, or that will lead to a decision to pursue a divorce.
The private investigator interviewed for the news spot said that his business has seen many changes since he started back in 1981. Back then there was no Facebook, cell phones or GPS which can all be a part of the investigation into alleged infidelity, as long as the investigator follows the relevant privacy and electronic communications laws.
For better or worse though, this investigator says that much of the time such high tech sleuthing in not necessary. Often the cheating spouse will be conducting rendezvous in public where they can be seen by anyone.
Source: Channel 26 Fox News "Cheating Spouses Lack Subtlety," Kristine Galvan, Nov. 8, 2011