Anal virgin until swinging

Let me start by saying don't judge Rob too harshly or the situation as it ended in me doing anal.

After trying a mfm 3sum over 4years ago, Mike asked if I would go meet our friend Rob alone. I said if that's what he wanted. I had never had anal nor was it discussed before hand. Our friend Rob was a nice 8.5in and very girthy. I was up doggy style on his bed and he started pushing me down flat with a pillow under my stomach. He had been in my vagina but otherwise had no lube on. He started putting it up my ass and I said hey stop Mike never does that. He simply said I'm not Mike. Then laid down on me and the weight of his body pushed a good amount further up my ass. It hurt bad and yes I cried some as he talked so filthy to me. I'm not sure why but when I heard him getting close through all of the filthy things he was saying it hurt less and I found myself having an orgasm when he started cumming in me. Next few times it was uncomfortable but ended in same orgasms. Now it's just something I love as a surprise and part of love making.

Thanks,
Beth