How do I classify this?

So I (f) have a brother 7 years older than I am. I think I was about 5 or 6 when this happened. I don't know how to process what happened or what to even call it. He never touched me. He never got me to undress. He never physically hurt me.

What he did do, while he was in charge, and the grownups were out, was get me to play a game called the tickling game.

He would lie on the floor, motionless, and I was supposed to win the game by making him react to being tickled. At some point he told me that if I tickled over his pants I would win because he was ticklish there.

Over time the game progressed to me tickling him under his pants. I remember he ejaculated once, though at the time I didn't know what that was. We had to flip the cushion on the couch to hide the stain. We'd get in trouble if the adults found out. Later he encouraged me to play the game with one of his friends.

Aside from feeling gross about the situation I don't know how to process this. He was not an adult. He would have been 12 or 13, and just have started puberty. I feel like I was complicit because it was my actions. A couple of years ago I read an article by an abuse survivor and it unburied some things. I wondered if I too, was a survivor, or if I was an impostor.

We are both adults now and it has never been mentioned, either between us, or (to my knowledge) to my parents. We have no shared interests and see each other only on special occasions. I also just had a birthday and none of my brothers acknowledged it (the younger brothers only realised when cake was put on the table while I was over my parents' place), and I'm feeling some feelings. Resentment being primary.

Before I broach the topic, either with him directly or with my parents, I want to be clear on what actually happened. That's what I want. Clarity.

Note: I have posted this on another platform before, but I used third person voice while anonymous, describing an elder child and a younger sibling. So many people assumed I was the elder child and I got a lot of hate. I already felt dirty, and it was not helpful.

I also realise the sounds like a lot of other rage-bait articles.I'm not looking to make people outraged on my behalf. I just need help making sense of it before/if I decide to bring it to light with family members.