When a man want to stray, it's sometime very difficult to tell if he's really stray.
An example:
This hubby came home on time. Does not always use his mobile. Even allow you to see his mobile phone etc. Went to sleep on time, goes to work as usual.
However, he actually have an affair outside during his office hour... Worst is with a colleague.
Such thing also happened. He's smart to delete off all messages after off work. Smart to 'clean his mouth after eating'.
But not that smart to make her wife suspicious by going to his office some day, and found out he's out for 'lunch' for more than 2hr.
Many possibility can happened. I will suggest to monitor him for time being. If suspicious rises, perhaps to engage a PI to follow him, or even get some 'stranger/friend' whom he doesn't aware about, to help in tailing him. Take note of his behaviour like his intimacy, sperm count, etc.
If he's really having affair outside, you have to think of what you should do to it. Many stay cause of kids. Some open an eye,. close an eye. Some 'revenge' by having the same. Some divorce etc