In my experience with my clients there are 3 main reason why a person constantly feels their partner is cheating on them. These are trust issues relating to past experiences or trauma, lack of confidence in themselves or they are indeed cheating. People that are lacking communication, connection and intimacy in their relationship are more prone to feeling that their partner is cheating on them. If your partner hasn’t given you any real reason for you to believe they are treating on you then it’s probably relating to either past trauma or a lack of confidence in yourself.
If you find yourself constantly worrying about your partner cheating then there are two things you need to do. First you need to discover why you feel the way you do and secondly you need to talk to your partner about it and explain how you feel.