Just hire someone to tail him for a week or so. Usually, if you have some suspicion thats a good sign that he is or your just paranoid.
You can find this easily, but you have to know all those he interacts with ; friends and colleagues and find out whom of those talks to him alot on phone. If you know their relation compare it with time on phone. Example if he pretend to talk to his colleague Sam alot but you know that his relation with Sam is not too much. This means he lies and probably talks with another woman.Is my husband cheating quiz?