I'm not really sure if this is what I think it is

So recently I have started to remember this "friend" I used to have. I started remembering this around the time I lost my virginity with my girlfriend. I kept remembering these "hangouts" my actual friend, lets call her S, and I would have with this girl, lets call her K, who was 4 years our senior. We were around 9 at this time. S's mom made us have a sleepover with K after K got bullied by S's brother. We went over to K's house excited, since she was the older cooler girl. There it started off normal, watching movies, eating snacks. Then K would start to touch us and ask us if we wanted to pretend that we were having sex. She undressed us and would touch us inappropriatly. I haven't quite remembered all the details but I remember K would come over and this would be a weekly occurrance. I was wondering what you would call this. It wasn't consented, but we thought we would get in trouble if we told. Should I talk about this with my therapist? I'm scared.