Naw its not creepy, gal dang if I had a dollar for every time I jerked off to a lurid picture of an ex I could retire and buy a small country
Lets face it, if you dated somebody you found incredibly attractive chances are your head is filled with all sorts of sexual images probably to sleazy for Larry Flint to publish...and quite frankly after all the hell some of my exes put me through they at least owe me a the occasional jack off to a mental image or picture. C'mon now. Kidding, no really...
Personally I really wouldn't let it bother you but if it does I'd recommend getting back on the horse and meeting somebody new to take her place, but honestly even then you might still think about her. Maybe find some REALLY good porn? I know that sounds tongue in check but hey if its good enough you'll keep going back to it and stop thinking about your ex so often. Or if you find yourself thinking about her and those feelings pop up dig it out and focus on it, at least when your done you'll look up and realize it wasn't her you've been rubbing one out too.
I don't know I hope it works out for you but honestly I'd just say kick back and enjoy yourself, your not hurting anyone and it really isn't that abnormal. Why not just try to have fun with it and let it be what it is until she fades from memory?
Best of luck