Did my inactions and wrong decisions cause my 16 1/2 year old cat to die? Please Please help me!?

God, give yourself a break! It sounds like you truly loved your cat & went out of your way to do everything possible for him. Loss is extremely hard, but he was 16 1/2 years old & I'm sure he lived a great life with you! I'm very sorry for your loss but please go easy on yourself!