Hun, I know exactly how you feel. But by expressing your insecurities & appearing 'not to trust' her will eventually do just that. If she thinks you don't trust her, she will eventually think 'hell why not? If he thinks I'm cheating then I might as well'.
I'm working on this myself at the moment, but being insecure will take tiny little steps to get over. Allowing her to go out & building that trust will make you eventually look back & think what it was you are worrying about. If she loves you enough, she will love you enough NOT to cheat on you. If she thinks your being too clingy, she will pull away. Let the rope loose a bit, not too far so that you can't see the end - and then bit by bit, let it out some more till it feels natural xx
Rich coming from me in my current state of affairs, but this was advice given to me - just a bit too late. I hope it can help you in these early stages xx
Some people come into our lives and quickly go. Some stay for a while and leave footprints on our hearts. And we are never, ever the same. -- Anon