Afraid
It wouldn’t be the first time that Mark cheated on his significant other. Even though it hadn’t happened yet to his wife’s knowledge, it didn’t mean that he wouldn’t do it. She was the person Mark cheated on when he was dating Nadia after all.
Getting Worse
In the beginning, these thoughts only came to Mark’s wife sporadically. It might have been possible that Mark was meeting up with his friends or held back late at work. However, these thoughts quickly started consuming her and she was constantly questioning her husband’s actions.