I'm still torn up over something I said when I was about 5-8 years old with my father
What did you say that could have been so bad?
I told him I didn't want him to be my dad anymore
If you are still feeling guilty you should go make amends and have a fun day out with your father. You can apologize to him and get it off your chest, and I bet you'll feel much better about it!
Nah I'm fine, I just lost it and had a tantrum.
I'm sure if you explain it to him that it was just an angry outburst he'll totally understand!  I think it's worth an effort on your part to resolve this so you stop feeling so torn up about it.