Was this sexual assault or whatever?

I’m 22.. this happened years and years ago maybe when I was around 12 or something close to that age.. me and my siblings and a couple of his friends were over(my brother) we were all playing hide and seek and everyone somehow was downstairs. One of his friends stayed upstairs and he was feeling on me. Tried to insert his penis in me and i literally didn’t realize that this was something that bothers me and was kinda wrong. He was way older like around 18 at that time maybe close to his 20’s.. I really wasn’t aware of what I was doing honestly I just went along with it but someone came upstairs and he hurried up to stop. I didn’t know what sex was bc I wasn’t exposed to it that early. So I’m now just sitting here thinking about it like I was kinda taken advantage of me being young and uneducated on it and I would have let it happen like a big dummy.. every time I see him I can’t stand to look at him, I always look away bc in disgusted now that I’m older. I never told my brother or my mom and i don’t think i ever will since it was so long ago.. was this actually wrong though?