All in the Family

So I'm riding the train and I got distracted from the car I wanted to ride by a person that wanted to buy an oil from me but got scared off by my prices. When I sat down I noticed a young lady having an argument on her phone. From what I could gather she was speaking to her soon to be ex-boyfriend. "How certain am I that they were breaking up?", you ask? Well, apparently her boyfriend had sex with her 19-year-old sister and the sister, feeling the shame, confessed it to her. So she is reading him the riot act but it sounded as though he was trying to deny that it happened. She then went on to elaborate on just how nasty this guy was for having sex with the sister. He also decided to not use protection. She didn't seem concerned about a pregnancy although her sister is apparently very promiscuous and she warned him that if he caught an STD that he "better not try to hurt her" for it. My assumption is that she is on birth control. She is also, apparently, in a group of girls that find sex a popular hobby. Now I was also able to glean that he was nearly 50 years old. From what I could tell about her I would figure she would have to be in her mid to late 20s (early 30s at the most). I would have to admit that the guy was a good looking, 40 something and was very charming. I also found that this was not the sister's first time cuffing her man. At this point, I would have to wonder who was more at fault here: the girl, the sister, or the guy.