Bad person?

So I was at a friend's house for their birthday party a few weeks ago and there was this hot chick there. We started talking and I decided I wanted to smash dat hoe. We went into my friend's bedroom and when I thrusting my big wang inside of her she mentioned that she was his sister. She said she felt like a badass by doing it on her brother's bed. She was hot AF so I kept going and finished in my friend's goldfish bowl. The fish started eating the semen so I hope that doesn't hurt them. Since then, I've started dating his sister and I smash her all the time. I don't plan on telling him since I think he will get mad. I feel like this stuff happens to people all the time but I wanted to make sure it's normal.