I've been sitting on this question for a good month because I wanted to answer it correctly. Knowing how much I fumble my words and what I mean, I probably never will so let me have a go regardless.
My first time would be to detach whatever connotation you have to being a "fat fetishist".
It's just a different term for that fat appreciation. Fat is ALLOWED to turn you on. I get turned on by fat on others as well as myself. It forms my entire sexuality.
You can appreciate fat sexually, that counts as appreciating.
Seeing fat women/men/NBs as purely sexual objects is a separate thing entirely.
Kink does not equate to creep.
I've noticed a massive wave of puritanical attitude when it comes to ones own sexual feelings in the last few years as people choose to eschew their sexual gratifications as opposed to approach them and unpack them. Is it easy to attempt to dispose of your sexual feelings instead of having a conversation with yourself critically about them? Yes. Is it better for you and your well being in the long run? No.
If you feel that your sexual gratification outweighs your appreciation then that is something you have to unpack within yourself. Perhaps you're giving sexual endeavours too much weight in your life (pun intended) and need to focus on non-sexual things until you achieve balance.
To be aroused by fat bodies is not mutually exclusive from appreciating them or being an ally to fat liberation/body positivity causes. You can do both. I have been doing both my entire adult life.
If your fetishism of the body is outweighing your appreciation then it is a problem with your attitude and approach to sexual gratifications, not to the body itself.