We are friends with benefits of almost 2 years. When I was trying to introduce my sister to him over the phone he got mad because I referred to him as friend. Then he got happy when I changed it to “boo” him and my sister met in 2 occasions. But my question is, why would he add my sister on social media (Instagram) and not tell me. Is this weird? Or did he do it to tea? Build a friendship with my sister? Get closer to me? Or try to have sex with her too?