Did I accidentally end my kittens life?

I lost my precious boy a few days before Christmas after 3 months of constant vet visits and driving hours across the country for specialist care. There was nothing they could do for him and he ended up losing mobility and seizuring and throwing up he was too far gone so I had to have him euthanised. I'm still traumatised and wake through the night in tears. I loved him dearly. He was a Devon rex and Ive never felt so much love for an animal before In my life. He kept pooping on himself and I had to keep bathing him like 2-3 times a week. I ordered tea tree oil cleaner and was washing him with that. I've just read that it's very toxic to cats. He previously had ringworm from his litter and this bottle said it treats and keeps ringworm at bay. I've just read the bottle ingredients and its for humans, not tested on animals with 100% essential oils! He never ingested any he was washed with it. But one review said when it touched her skin it really was strong and affected her muscles and made her dizzy etc. Did I do this to him???? I am absolutely devastated. Please help