let me save you some time.. If they delete their texts they are cheating. Delete their emails, guard their phone like a dog with a bone, have a code lock on their phone, become defensive when you look at their laptop or phone, refuse to give you passwords to their accounts, or spend bizarre amounts of time driving around in their cars (an hour to go a block and get milk), or if they are "just being nice" to the divorced neighbor down the street....they are cheating.
The list goes on and on. Always trust your instincts.