It's true. You did nothing to make him do that. His actions were his choice, and his alone.
Everyone knows people are not supposed to hit and rape kids. EVERYONE knows that. He knew that. He knows it was against the law. He probably knew it would hurt you. He chose to do it anyway, for the sake of his own needs.
It sounds like he 'groomed' you. He was nice to you. He took you out for icecream and made you trust and feel safe with him by getting you to talk about the problems with your stepdad. Most teenage boys / young adults really wouldn't be all that interested in doing that with an eight year old kid. There is a small subgroup of people who do though - including those who purposefully seek out and befriend young children with the intention of eventually having sex with them.
Why did he do it to *you*? Most likely because he had the inclination to have sex with a child and you, through no fault of your own, happened to be available. If it wasn't you it would have been some other kid. He probably DID do it to some other kids. But it wasn't you, it wasn't your fault, and it didn't happen because of anything you did or did not do. It happened because he is a child molestor, and he wanted to have sex with a child. He simply didn't care about the law or the affect it would have on you. He thought only of his own gratification.
I am so sorry it happened. My brothers were raped by our father, and I know how much it hurt them. Like you, for years and years and years they believed it was their fault - that they did something worng, that they provoked him, that they aroused him... but it wasn't their fault. It happened to them because our father was sexually attracted to children. It happened to you because your babysitter was as well. It is ALWAYS the adults fault, without exception. Even in the occasional instances where a child provokes or even comes onto an adult (usually because of prior sexual abuse) it is the
adult's responsbility to act within the law and protect the child. There are no instances where a child is at fault or held accountable for an older person having sex with them at all. The older person is always to blame.
It is possible to heal from this. It can take a long time, but it can be done. You are not to blame and I hope you can find a way (through therapy maybe?) to let go of the self hate and rage and shame. You were just an eight year old kid. Eight year old kids are so young, so little, so in need of protection from monsters like your babysitter. Stop blaming that eight year old kid, that eight year old you. It really sounds like he could do with some love and protection instead.