Essentially the title. My brother (23M) and his gf (21F) have been dating for about a year now. I recently went to a party with her sister and some friends. I knew my brother didn't care if we hooked up but his gf asked me not to. I told her I wouldn't try to in kind of a backwards way of answering her request. When we got there, we did some X and some other stuff and by the end of the night had hooked up. Neither of us are interested in anything serious, but she seems to still be interested in playing around. One of our friends told my brothers gf and now she's mad, but my brother doesn't care. When I asked her what the big deal was (not like we're related and they're not even married or engaged) she wouldn't answer me. She's not Christian and neither am I. AITA?