Grouped
I was 15 years old when my brother grouped me in the shower. I didn't know how easy it was to open a lock just by pushing a pin through a little hole. I was soaping up when he sneaked in with his friend and grabbed my boobs. "No used screaming" he was telling me because my Mom was in the super market. I was so embarrassed when he told his friend "don't you think my sister has a nice pussy" I was so frozen with shame about being naked in front of him and there wasn't much I could. I was so utterly embarrassed I never said anything to my Mom and they got away with it.
You can still get him back. Get him alone and suck him till he cums. Steal his cum down your throat. That will show him!!
Good thing you didn't tell your mom. Would've been a shame if he got in trouble for something so innocent.