Here is something that you MUST accept... If she is going to cheat on you, raging jealousy will only speed along the process. It certainly won't stop her. You have to develop the attitude that "if she's going to cheat on me, I want it to happen." That way you can move on to better things.
Yes, as with anything, sometimes a person will respond well to you showing a little emotion. But trust me, you are MUCH better off never being jealous than searching for just the right amount of jealousy.
The reason is that jealousy automatically signals insecurity. And nobody wants to be with someone that is insecure. Girls want to be with the catch, the prize, someone who knows he's got a lot to offer. They don't want to be with someone who thinks she is going to leave him for every guy she talks to. And here's a hint, if you let her know you're afraid of her leaving you, then she probably will.
You must keep your life that you had before you started dating. This will help tremendously with jealousy. Jealousy usually comes as the result of not having any other options. When you are that afraid of losing someone, every little thing can be seen as a threat. So you have to keep your life outside of the relationship strong. I'm not saying you should keep other girls on the line, but you should know that you can go out and get another girl the next day if you have to. If you have a great life, you won't freak out over the little things, because you will be fine no matter what happens.
Put yourself in her shoes. If you talk to someone of the opposite sex, it doesnt mean that you are interested in them. The same goes for her. Just because she has friends of the opposite sex, or talks to them occasionally, doesnt mean that she is going to cheat on you. But if you throw a fit every time she does it, it might actually push her away.
So keep your mind off of these paranoid thoughts by staying busy with other interests, and looking at things outside of your emotions. If you can keep this attitude, or at least act like it. You will be more attractive to your partner and your relationships will prosper.
