A current PhD applicant in a dilemma between current lab and other programs
I would suggest that you be as open and honest with your current supervisor as you can. No surprises, no evasion. Tell him your list of schools. Tell him you want to aim as high as you possibly can. From your current A+ school, possibly to an A++ school.
I have known some students in your position. A student who excels under a professor makes the prof look very good. If that student goes on to one of the very tip-top schools after working with the prof, the prof's reputation grows. Maybe he is sad to see you go, but he should also be glad to see somebody he taught go on to Big Things.