I think attempting to repress insecurity often has the side effect of making insecurity worse! I think this is something that talk therapy could help because the way you perceive the world has a lasting effect on more then your partner. I also think talk-therapy is helpful in general because you may not be learning the skills necessary through talking w/your girlfriend to help you ease your insecurity.

Remember that she is not your therapist and she will not always be in the frame of mind where she can help you help yourself.