I can't deduce if someone is hiding something or not by what they say. Don't even try. It does seem out of place for someone who said you could check on them, or someone who knows you're going through a period where you check on them, though. Typically, they say, cheats get indignant with you if they catch you "invading their privacy", if you want to use that as a measure of behavior.
I think there's more to checking up than calling him. I think you need a 24 hour itinerary, and the phone numbers where he's going to be at. Checking phone records isn't going to help since he knows you're checking phone records. They're going to be clean even if he is still cheating. Keep your eyes and ears open. If he's lying, sooner or later you'll catch him in one. It's difficult to remember all the lies and have them harmonize with one another.
