My son always pushes limits

My son will be seven in January. I have a hard time ever playing with him because every time we do, she gets overly excited and ends up crossing lines. It usually ends up with me getting hurt because he gets overly excited and we’ll hit. He crosses boundaries with his sister sometimes but especially with his father and I. Tonight we were messing around and he was sitting on the bed. He laid down and grabbed my butt and then stuck his finger in my butt hole. I reacted by slapping his like it was a genuine reaction. I told him that he was out of line and knew that he cross the limit and unfortunately playtime was over because it he had gone to far. I feel incredibly violated and well. I don’t think there was anything sexual behind it, I just feel so disappointing because I don’t know what to do. We’ve had several talks about touching people in their private areas. But more importantly, he always ruins the moment by going too far. How do I addresses? I told him we would talk about it tomorrow. I feel infuriated, sad, violated, and more importantly, it really discourages me from wanting to play with my son, which is heartbreaking to me.