The best thing to do it to accept situation or you will miss much of the life happening around you, while reprocessing the old great bits about her. By resisting to her you are reducing your inner feeling, capacity of love for others and possibility to meet a new girl, which might be even better than this. It is just a mind game, which we all get trapped in life: things we cannot have make us addictive and can become self-destructive to us if we aren't aware what is causing this to us.

In either case, you won't get her back with this kind of mindset, so its not rational to keep this mind loop, although I know its not easy to break the pattern.

I would recommend reading some books like "Mastery of Love" by Don Miguel Ruiz. Put your mind to rest and open the eye for the other joyments of life.