Has she recently changed the password on her phone or computer?
Has she started talking about a new male friend at work, or a cousin you've never heard about who just moved nearby?
Is she suddenly busier than usual, with no explanation of why?
Does she have friends that you're not allowed to meet or spend much time with?
Has she become more jealous or suspicious that you might be cheating?
Has she been wearing or buying nicer clothes that she only seems to wear out of the house?
Has the amount of eye contact either gone up or down?
Does she initiate sex less frequently than she used to?
Is she a thrill-seeker?
Has she cheated before?