Life is too short to be stressing every time your girlfriend goes out with her friends. Let your girl live!
A healthy relationship means trust. It means respecting one another's privacy. It means being secure with yourself, and confident your girlfriend knows what she has.
Jealousy truly is a wasted emotion. 90% of the time, it will be unfounded and only serve to create issues where there were none. This year, resolve to do away with imaginary fears and doubts, and you'll reap freedom from insecurity and renewed satisfaction in your relationship.