I got so much stress from what he had done to me and I feel like my life has been messed up since he molested me and did bad things to me. My childhood was full of memories of him. And I’m pretty sure he did those behaviors with sexual purpose because I knew that he enjoyed it. Just can’t believe what had happened to me but that disgusting feeling was so real and true.
Bellaellawhatever... oh how I relate to so many things you've said in your post... I totally get where you're coming from.
It sounds like you're dealing with what I imagine so many others who've dealt with cocsa deal with (including myself) - that extra layer of denial and guilt about what happened because the person who did these things to you was a child...
If a boundary is violated, it's violated. And your body won't know the difference between whether that's an adult or a child. All it knows is that it's been violated.
You're asking whether it was abuse. This is something I have struggled about my own cocsa for years. I've come to the conclusion that the word 'abuse' can be difficult to ascribe to self experience for people who've experienced cocsa because it speaks of 'intent' to harm by the other person.
So with cocsa there's an issue with this. Being a child themselves (the perpetrator) they can't have had the same level of intent to harm (if any) as an adult. And so (I'll speak for myself), I'm left confused as to how I can feel so damaged by a child who never meant to hurt me.
But the intent behind the child who commits cocsa can be to do with them needing to play out their own dynamic of whatever is going on for them. E.g their own abuse (and btw if this child was watching porn - that is a form of csa). Essentially they seek out someone to USE to do what they need to do - explore and get sexual gratification. Maybe play out power dynamics. (You say yourself his aim was for sexual purposes. So child or not, you feel you were used for someone else's sexual needs).
So you see, your body doesn't really know the difference about who hurt you. But does know that you've been hurt. You felt used and objectified for someone else's gratification and this has caused you to suffer sypmtoms of csa. Funnily enough (and I relate) you simultaneously say you experience these csa sypmtoms as an adult but can't actually connect to this experience as being abuse because the person who did it to you was a child.
One very helpful video for me (youtube) is 10 facts about child on child sexual abuse by Kati Morton. Look it up - I think you'll find it helpful.
Be gentle with yourself.