Most people suspect their mate is cheating because there is a change in their behavior which they do not like.
If you found out your mate was NOT cheating but the behavior remained it is unlikely you would jump for joy. When someone wants to find out if their significant other is cheating they do so to get an (explanation) for the change in their behavor. Other times it's to feed our ego or prove we aren't insane by busting them because they have denied cheating or labled us insecure...etc
There are numerous ways that people snoop on their mates by going through their cell phone, emails, wallet, hiring a detective, installing a key logger device on their computer...etc
However the bottom line is if you are (unhappy) in your relationship or you (don't trust) someone it's okay to end the relationship for those reasons alone!
Save your time and money. Trust your instincts! "If something doesn't feel right to you then it's probably not right for you."