The issue you're facing is that you don't want them to hate you because you will need their references and blessings for b-school application reference letters. One way to to avoid the hate is definitely to tell them in good advance that you are leaving so they can find replacement and adjust to it, and as long as you do that and tell them straight up that you want to take the next step, they have no right to be upset. If they are a spiteful sort though don't tell them too early, maybe one or two months before you're leaving, but if they are then you have a bigger problem, and that is finding someone else to write your recommendation letters.