Below are some of the most common signs of infidelity:

• Your spouse is spending more time away from home, perhaps going to places where he or she is difficult to contact. Common excuses include unusual errands, conferences, seminars, working late, business trips, fishing or hunting trips, or visiting old friends. They may find a reason to begin attending functions and events alone.

• Lack of interest in sex or a suddenly increased interest in sex, perhaps with new or unusual sexual requests. At the beginning of an affair, sex may increase, but as the affair goes on, sex in the marital relationship will often wane. In a long-standing affair the cheating spouse may begin making excuses to sleep in a separate bedroom. For example, John recalls that his wife "...said she couldn't sleep with my snoring and moved into the guest room. That was three years ago. At the time I felt guilty and wretched - I tried every snoring solution on the market! But now I realise that she moved into the spare room for other reasons - her affair was already in full swing, even back then."

• Their behaviour towards you changes? For example they become more or less physically affectionate than previously. They may be more critical of you than previously? Or they may have stopped talking about the future?

• Changes in appearance or personal care. These may include showering more often, dieting, becoming much more interested in their appearance and grooming, beginning to attend the gym, or buying new clothes in a much younger or smarter style than they have worn previously.

• Your spouse begins to listen to different music or watch TV programmes that they have previously ignored or disliked. This may be the music their lover enjoys, or the TV programmes they watch together. Noelle was puzzled when her husband began watching a soap opera he had previously said he hated. She explains "He began watching every episode and at the time I just thought it was a bit odd, but later I learned that his lover was an avid fan of the show."

• Other physical signs include returning home smelling of unfamiliar perfume or aftershave, jumping in the shower as soon as they return home, or returning in different clothes to those they went out in. More obvious physical signs include unusual scratches or love bites, as these are almost impossible to explain away innocently.

• Seeming much more distracted than normal or daydreaming more. Jeff recalls "My girlfriend Helen was always busy, we used to joke about her being in perpetual motion, but suddenly I began finding her shut away in the bedroom daydreaming, with love songs playing in the background.  It wasn't anything big it was just out of character. Once I walked in on her looking thoughtfully at a map, I tried to talk to her but she just shrugged it off. I have no idea to this day what she was doing with it, possibly planning a trip with him? Shortly after this I discovered she was having an affair with one of my closest friends."

• Your spouse suddenly loses interest in household tasks or is he or she spending less time with the children.

• Secrecy - if your spouse turns off the computer monitor when you walk into the room, or quickly ends a phone conversation this is a sign they have something to hide. They may also go outdoors or into another room to talk on their mobile phone, or turn their mobile phone off when they are with you . Some cheaters have a secret e-mail address that allows them to communicate with their lover without fear of detection.  Others may begin deleting emails and phone messages so that you do not have chance to read them. 

• Bills can also provide some important clues. These might include unexpectedly high phone bills or credit card bills, where some of the charges are for shops, hotels or restaurants that you and your spouse don't normally frequent, as well as unexplained charges on a bank statement. Some cheaters will have a second mobile phone that they keep hidden in their car or office, or a separate credit card that they use to hide the costs of their affair.

• Your spouse has someone else's house keys or garage door opener without a good explanation.

• You find strange personal items in your home when you return from work or from a trip away. Or you find items that do not belong to your family in the car. These are sometimes left on purpose by the cheater's lover.

• You find emails, letters, photographs, texts or social network messages, that suggest an affair. We'll be looking in more depth at  internet infidelity shortly.