My friend is mad I slept with someone she did.?

I started a fwb thing recently with a guy who had pretty much a one night stand w my friend in december she found out last night I had w him and told me its scandalous bitches like me who cause her not to hang out w chicks and it doesn't matter the extent of chicks and it doesn't matter the extent of her relationship with him its the principle I had with him. her relationship with him its the principle her relationship with him its the principle I had with him I told him she was tripping out on me and he said that what we do needs to stay between us (agreed). I didn't go out of my between us (agreed). I didn't go out of my way to tell get she had asked me if I was taking to him and then demanded to know if wed hooked up. I honestly dont see the fuss in it he was never her man and they hasn't even talked in two months. he told me what the did vs what we did wasn't even on the same level. supim just wondering am I really in the wrong or is she retarded