That's hot!well sort of... my brother and I share a house. Well, he pays for it and I help look after it. He works away alot, so one day when I thought we were home alone, my boy and I started playing around. I got to being topless and in the missionary position on the couch when my brother walks in on us wrestling. Lucky I was still wearing jean's. All he said was "are you 2 right"? in an Aussie masculine accent. I had to make up some excuse about needing to wash my top because it had a stain on it. I went and put another top on and he went on with his day. I think he probably suspects something maybe going on between us but he's probably not sure and he's never asked me.
I wonder how he would have reacted if he'd found you two during a good fuck.