Here is another theory. Instead of cheating on him or being a summoned beast herself, she does not really exist. Or the MC doesn't really exist. Okay, he has coworkers, but maybe he is just a being, that has been created some months earlier with fake memories. And the memories of his coworker and his position in his working place has also been newly created. As his wife is a fake existence (maybe a golem of sorts) there is next to no interaction. Maybe that's because faking the memories of a real marriage on a women would be too much.
In short: She is a robot.