My 22 years old sister broke up with her boyfriend last year(my parents knows about this), but this year, when I'm with her at the library computers, I'm still seeing her messaging with him on Facebook again and my parents doesn't know about the messaging. The thing is that the guy created a fake Facebook account just to message her secretly. He is hiding something... I asked his friends if they know that he is still in a relationship with my sister and he says 'no, they are not together.' He secretly comes over to our house every week when my parents are out, and they have sex.... I'm in the house too, but I'm hiding in my room and I pretend don't know notice him in the house. The reason he created a fake account is because he is hiding from his friends. Most likely, this is a 'booty call'. I'm not sure if this is my business and not sure if I should tell my parents because she's an adult. I don't feel like talking to her about this. I didn't say I don't like him, but I just wish he's not around my sister.