L.S.
Why don't you just explain to him the way you just explained to us? Sounded pretty good to me... Just tell him about the stress levels, the kinks you are in the middle of working out, and ask that he hold his opinions to himself, at least until which time you can handle it again, and tell him that you don't want anything to come between the two of you. I am sure that even if it doesn't seem like it, he is doing it out of love for you. Even if the way he is doing it is causing you to stress, maybe he is just dealing with the fact that you are not living the exact way he had always planned you would.
I had to go back and add in here that the whole "cut him off" comment really upset me... he is your father after all... I can't beleive how willing people are to "drop" family members... and then we wonder why things have changed so much in society... people don't hold dear what is truly important in life!
Good luck, take a deep breath!