There are a lot of different signs you can take note of to see whether your girlfriend is cheating on you. One of the biggest signs you can look out for is a sudden change in her behavior, coupled with a decrease in your physical/sexual activity. If she’s pulling away from you physically or emotionally, and you sometimes catch her lying to you, then something must be up. Just remember, these signs all depend on what type of girl she is so they aren’t that foolproof. It’s all up to you and how well you really know your girlfriend.