It's not cheating at all. Your girlfriend should be proud that you'd rather touch yourself, than be with any other woman.
Then again, some psycho controlling girlfriends think it is cheating. So you should probably check in with her if your relationship is "sexual" in nature. But from my...
...experiences with myself...? Some people say they have "first-hand experience" with sex, therefore know more about certain things than I do.
But I have experienced with my first hand AND my second hand, and personally I know my hands better than I have ever known a girl.
So is experience...