There are several signs that a girlfriend may be cheating on you. You cannot rely on just one of these signs alone, but the more signs you see and the more you suspect, the more likely it is.
If you have a girlfriend who suddenly won't show you any sort of affection, she probably feels guilty about it. As David Deangelo once said "Atraction is not a choice." Women feel attracted, and sometimes they're in a rough period of time with either you, or themselves emotionally. The more emotional they are, the more vulnerable they are to cheat. If Any of these signs are noticed during a period of time AFTER something emotional such as an arguement that went too far, or a time when your girlfriend had something happen to her, it's very possible. If your girlfriend ignores the topic or changes subject, this is deflection. Whatever you are talking about, she does not want to talk about, likely because she's hiding something.
Perhaps the biggest indication is body language. Women who really feel the need to tell you something, but are stopping themselves, make a "shushing motion" usually just leaning against their fingers. Covering of the mouth is also a sign. If women show shame, they will push the two fingers (pointer and the middle) to their thumb and look as if they're grabbing the side of their forehead. If you watch the TV show "Lie to me" you will be able to better understand body language. Otherwise, you can read books by Joe Navarro about body language. He is a former FBI agent who specialized in behavioral assessments. He uses science to study the brain and how the limbic system responds during certain emotions, which lead to certain behaviors that happen naturally.
A woman who avoids eye contact when she normally always makes eye contact is also a sign. A woman avoiding talking about herself and what she was up to, suddenly becomming more vague, or just avoiding talking altogether is likely someone who may have cheated.
Some other signs include appearance. A woman will generally dress up more often than usual if she has been cheating. This includes when she's going out as well as staying in with you. This is not so much that she wants to attract other men, and her intentions may actually be good, but after cheating on you, she will not like to look at herself in the mirror the same way, and she will pobably put on more makeup.
The signs of her cheating are always there if you are willing to accept it.
