A divorce attorney reveals the 3 biggest mistakes married couples make

It's important to resolve disagreements right away and not let resentment build. Polland recommends taking time in the evening to right any wrongs that may have occurred during the course of the day.

"There's an old saying, 'Never go to bed angry with each other,' and I think that's true," he said. 

"You have to be diligent in making sure that your relationship with your spouse hasn't gone awry," Polland said.

He described "aberrant or unusual behavior," such as changing passwords, making or receiving calls at hours that don't seem appropriate, or a sudden wardrobe overhaul, as tell-tale signs of an affair.

"Sometimes if you catch it early, you can resolve the relationship," he said. "The longer that extramarital relationship continues, the harder it is to unravel it."

"A lot of times people choose somebody for the wrong reasons," Polland said. "You've got to have a solid foundation in the relationship so that the relationship can continue when some of the other factors start to erode."