I got fucked by my boyfriend's twin brother.....

My boyfriend lives in his parents house with his twin brother, his parents are away a lot, they travel a lot, I often get them mixed up and there have been times when I accidentally slapped my boyfriend on the butt and it turned out to be his twin brother, we joked about it and laughed, one day I came home from college and my boyfriend's twin brother was in my boyfriend's room for some reason....... I thought it was my boyfriend and started hitting on him, we started having sex and I noticed that the sex was completely different, I literally fainted from orgasm, no one had ever fucked me like that, after sex my boyfriend's brother got up and went to his room and only then did I realize what had happened...... 20 minutes later my boyfriend came home, he doesn't know about it of course, but I can't get this best sex of my life out of my head.....