Boyfriend girl bestfriend moved in

I recently started dating this guy and he has a girl bestfriend from childhood. She moved in with him a couple days and he won't say why. He just says that her dad did something fucked up and police are involved. I guess she's not TOO much of a problem because she stays in her room but I just hate how I'm left in the dust. He now has a girlfriend, he moved another girl in his place and won't even say what her dad did that would justify her moving in with him. I understand it's her business but she's living with MY boyfriend.