We have all felt jealous at some point in our lives. Maybe it's the way your partner seems to have fun with a mutual friend or when they stare at someone attractive a little too long. It is never a good feeling. When you start to blame these feelings on your partner's behavior you are creating a problem in your relationship. Many times the very same quality that made you fall in love with this person is thing that is now the problem. They have a great sense of humor, are really good at conversation or are charming. Now they are too friendly or flirting and in your mind you begin to imagine worse. If you do not have knowledge that they have cheated or said or done inappropriate things (sexual or romantic) then you need to find a way to let these thoughts go and not act on them. Knowing where these fears stem from also helps. For many people it is having been cheated on in the past. For others it's a negative belief that all men or women will be unfaithful at some point.
There is a very big difference if your partner has been unfaithful. If you are in this situation then these thoughts and feelings are a signal that you still do not trust your partner and need more from them to help you get past whatever happened. If they have done everything they can to regain your trust it may be a matter of you taking that leap of faith and again letting these feelings pass and not acting on them. If on the other hand there has been no cheating then you have to realize the damage you are causing by accusing your partner when they have done nothing wrong. This usually pushes the person away from you and causes a viscous cycle. You accuse them, they get angry and become more withdrawn. You feel the distance and this makes you anxious which in turn makes you more suspicious and you again make accusations which further push them away. Despite your anxiety and certainty that they are doing something wrong, you have to first and foremost stop acting on these feelings. The impulse to lash out and accuse is the first place to start. Along with this beginning to examine your assumptions is crucial in stopping this cycle.