Kira, I would look very closely at that part of your hesitation to go out with Ken that is due to your worry about the potential response from John.

That you are unsure that you would be able to handle Ken's not being as physically attractive as some other men you know or have been with is completely normal. You can figure out for yourself whether you can overlook that flaw of his. No issues or concerns.

That you worry about John's response so much is not normal.