Oh yes, I think most of us have said, "What if" and "If only I knew".

Gary, obviously there was some underlying illness that BJ had that you just did not know about at the time, but when you finally saw evidence that something was wrong, you acted quickly. Unfortunately, it was too late and IT WAS NOT YOUR FAULT.
You know how good cats are at hiding some illnesses that get by the best of us, until it's too late.

You gave him the best 2 years of his life, loving and caring for him and that's what counts.

I know how much you miss your beloved BJ, but one day you will meet again with this precious boy.

Rest In Peace dear BJ.
You were dearly loved and will never be forgotten.