This seems odd. Don't people in the entertainment business usually change their names before they begin their careers? It seems rather counter productive to become "mildly famous" with one name, then have to start all over with a new name.

But even when entertainers do change their names, aren't they often just "stage names" while they retain their birth names legally?

Seems like someone else made the best suggestion regarding your personal situation. Only your GF gets the "real" you. Everyone else only gets to know the "stage name" you. If she is unable or unwilling to play along with that and call you by your new name in public, then I would question how much she really cares about the "real" you. Because the real you isn't just a name.