Infidelity within a marriage can be a devastating blow and can have long-lasting negative consequences, especially if there are children involved. Ideally communication within a loving marriage should be open and honest, and any issues should be able to be worked out without deceit or dishonesty. However, there are clearly times when partners are unfaithful, either on a spontaneous or long-term basis, and many times the other partner remains unaware of the infidelity. There are signs that may indicate a spouse is being or has been unfaithful.
A lower level of engagement and interest in your life than previously may be a sign of cheating. If your partner has complained about you drinking with friends or watching lots of sports but now doesn't seem to care, this could be that she has new interests elsewhere. If she turns away from affection or seems less interested in sex, these could be worrying signs as well.
Odd and unusual behavior that is out of character or breaks with routine can be signs of an affair. Unusual work patterns such as working late where before she never did, work trips away when this was not previously usual, going out with "the girls" a lot more -- all could be signs of an illicit relationship. Buying new clothes or lingerie or a sudden interest in exercise or weight loss can indicate she has a new interest.
Women generally want to communicate a lot of their thoughts, feelings and activities to their partners but if they suddenly don't seem as communicative as before this could mean they have found a new friend to pour their feelings out to. If they become withdrawn and give vague answers to questions and shut off conversations abruptly these could be danger signs.
In today's world a lot of relationships are conducted through technology. If your wife is spending lots of time on the phone and doesn't want you to hear, or is vague about who she was talking to she may be cheating. A lot of time spent on the computer or in chat-rooms, or new security or privacy settings can also be suspicious signs. And, of course, many a cheating spouse has been caught by a partner discovering texts messages or pictures on phones or emails and other messages.