Chances are if you are suspicious he probably is..
Exactly. I think if someone is being cheated on they probably know it.
Also remember, cheaters don't just cheat in the night. If they are a cheater, it could be 24/7. Someone could work 9-5 and come home to you every night. They could be cheating during their lunch hour.
Oh and this video is also a very good test if someone is cheating. Try it some time. I'm thinking of making this my new ringtone. Warning, language NSFW!