"The Cheating Boyfriend Test - How to Catch a Guy Cheating" is a great free article about spotting a cheater from a mile away. Rye McKeever outlines an awesome three-pronged test for your boyfriend's behavior. If he's not getting straight A's, you should probably look a little closer about what your man might really be doing when he isn't with you.
"The Cheating Boyfriend Test - How to Catch a Guy Cheating" doesn't claim to be a foolproof way to test for cheating, but it is certain to get you on the right track to finding out if your nagging worries have an underlying justification.