Apparently the proof, or at least some of it, is in the book. The co-author has said that he has seen the text messages and emails personally which suggests this stuff wasn't made up or forged. He said he does not know if Pitino knew of it though.
Also, Jaquan Lyle has said that he did see strippers in the dorms but did not see any sex. Apparently in the book, the madame (as she calls herself) listed about 12 player's names but said that not all of them participated.
Mike DeCourcy at The Sporting News thinks UL may try and self imposed ban to help get this case closed quickly. Not sure how this will play out but I know there is some legal investigations going on due to the "madame" stating one of her daughters was 15 at the time, which is underage. I think she may have something to worry about herself.