Wow, dude, you are a danger to that kid. Invest in some self reflection now. Nobody gives AF about your trauma if you use it as an excuse to be an absolute fucking monster and traumatize someone else. It sounds like you got off easy by only being banned from some family events. I would never look at you the same if you were my relative.

Beyond being a horrible semi uncle. If this behavior had been told to someone with a duty to report your not quite niece’s family could have faced a serious investigation.

One more thing, if you have a “sour” relationship with an 8 yo, YOU are the problem. They are 8, and at this point you are a fucking adult. I guarantee you your family didn’t get the full story from her, you better hope they never find this post and connect the dots.

Get some counseling now, what you are describing is abuse - get help breaking the cycle of violence you are in.