They often have a new found interest in their physical appearance; they get a gym membership or start working out.
Shuts off his cell phone when you are around.
They often lose interest in domestic activities; spending less time with you or your kids, stop working around the house, etc.
They become more defensive, pointing out your faults and blaming situations on you as a way to justify the affair in their mind.
They may have a sudden change in sexuality, turning down your advances or requesting more sex, and possibly desiring unusual or extreme sexual situations.
They may begin smoking cigars to mask other odors or scents.
Names of strange locations may begin to appear on your credit card bills. These names may appear to be restaurants, but you won’t find them in the phonebook. Often these charges are from Gentleman's Clubs or, as they are better known, Strip Clubs.
They may change cologne, clothes, or switch from boxer shorts to bikini underwear.
Their cell phone rings and they don't answer it.
They may get a post office box and not allow you to have a key.
They will often avoid contact with you when they come home. Often changing clothes and showering before they allow you near them.
They will become more secretive with money and spending, often producing unexplained credit card charges or withdrawals from the checking account. They may also hide credit card bills and receipts.
They may buy a new wardrobe or a lot of new stylish clothes.
They may have physical clues of an affair, such as make-up on shirt collars, perfume odors on shirts or jackets and secretion stains on underwear. Or you may discover notes on pieces of paper, phone numbers, receipts, condoms, etc.
Their driving pattern may change. Taking longer to get home, making stops to pick up random items (as an excuse for their absence), unexplained mileage or excess fuel consumption.
They may receive random phone calls at odd hours, or have conversations where they are whispering into the phone, in addition to short nondescript conversations in your presence.
There may be unexplained, repetitive numbers on their mobile phone bill made shortly after departing from home or returning to home. Most cellular bills provide itemized lists of all incoming and outgoing calls so they are easy to check.