Has he changed the style of his underwear? The way he does his hair? Is he suddenly dieting? Has a new hobby or sport? New smells on his clothing. Seen anything that doesn't belong in his car? Has his level of affection and intimacy with you changed? Is he being withdrawn, picking fights, or being too cheerful?
Is he suddenly funny about his phone? Deleting messages and e-mails off his computer? Destroying paper receipts? Clearing his phone's call log? Is he getting messages that are obviously coded, so that they mean nothing to you? From phone numbers that aren't in his contacts list?
Look for evidence on his mobile or credit card records. Like petrol bought away from his regular routes, lunch bought locally when he was supposed to be on the road, and calls made at strange times of the day or night.
Any of that and you or one of your friends will see something conclusive soon. Like spotting him with someone unusual, somewhere that matches a dubious credit card entry. It'll happen, believe me. The world's a lot smaller than it seems.
So if nothing like any of this is going on, you can definitely relax.
All the best,
Chris