Yeah, if you fear that your husband is cheating, then there is a real problem with your relationship that needs to be fixed more than you catching him or spying on him. State your fears to him directly and ask him what happened in the relationship that caused it. Do not do this in a confrontational or aggressive manner; that will only cause him to become defensive, evasive, etc, etc. It may be that the way you communicate with your husband, or your actions, are interpreted differently by him than you think. Not saying women cause men to cheat, but both sides harm the relationship enough that one tries to justify drifting. If someone isn't getting love and affection at home, they will find SOME way to get it.
Either way, if you have any plans on staying with him, then spying on him is not going to help rebuild trust in the relationship. Act like an adult.