There's an applicable car commercial out there. It says: since when is it a crime to leave the office ON TIME? or something like that...point is when did it become a crime to want another job???? You need to do what you need to do to get the job you want! I guarantee you, your employer would dismiss you in a heartbeat, if it were the best thing for him.
The days of loyalty are long gone and not that it is a good thing, but it is the way it is! Please stop feeling guilty and two faced. Do whatever it is you need to do to get that different/better job! Good luck!