One major source of tension in any romantic relationship is the possibility of cheating. If you suspect that your significant other is not being faithful to you and you confront him about it, that situation only becomes exacerbated if you suspect that he is also not being quite so honest with you about it. Thankfully, some tips exist that can help you determine whether or not you believe your partner.
Look for the amount of details given. If you catch your significant other off-guard regarding cheating, you most likely will notice that she won't have a lot of details to back up her stories and excuses. This is due to the fact that she most likely didn't anticipate your confrontation and therefore didn't have enough time beforehand to think up an elaborate excuse. On the other end of the spectrum, if too much detail is given, it can also be a sign that she was prepared for the confrontation and overcompensated with excessive details to unimportant things (such as what she was eating in the car when she was driving home from work late one night).
Notice any squirming and fidgeting. Squirming and fidgeting are two red flags that someone is feeling uncomfortable and put on the spot. If you notice that your partner is unable to sit still and keeps playing with his hands or with objects surrounding him, he most likely is extremely nervous and anxious about the topic at hand.
Watch for stuttering. Stuttering and stammering are two major indications that a person is experiencing some nerves and therefore having a problem putting together a coherent sentence. Be on alert for vocalized pauses, such as "um" or "uh," as both could indicate that he is simply trying to buy time because he is not sure what to say upon being confronted.
Check for unusual body language. Some small gestures can indicate that a person is lying, such as rubbing of the eyes, insufficient extended eye contact, patting the nose, concealing the mouth area and touching the neck, throat and collar area. All of these physical signs point to discomfort, and, in some cases, guilt and shame (such as the eye rubbing, which shows that the person needs to look away). Sweat beads can also indicate nervousness and anxiety.
Look for defensive behavior. If someone is on the defensive when confronted about cheating, it can be a signal that she is overcompensating and that she is angered about the questions that you are asking her. In many instances, you might also notice that she will reverse the topic and try to make it so that you are the one being confronted about cheating.
Observe any vocal changes. If a person is lying, he will often speak in a pitch that is significantly lower than his normal voice. He also might mumble and speak faster than normal.