Fucked my friends sister

After a night out with my best friend he said let’s go to his sisters house to crash, I was horny his sister opened the door when she welcome hugged me I discreetly grabbed her ass she loved it. We had more shots my friend passed out on the couch I sat next to him he was passed out. She came next to me and grabbed my cock, I flopped it out she started sucking my cock infront of her brother. I got really horny and wanted to fuck her I started fucking her right infront of him. She was loving every minute of this. After for a few month we started fuck discreetly on a regular basis.

Is that a bad thing?