This is a very difficult situation to be in. It sounds as if this guy is taking advantage of your friend. Some of these guys on dating websites know how to play with young girls' insecurities and needs – making them feel loved and happy that somebody finally understands them. You need to talk your friend out of this, make her see that he is using her and it could turn into a dangerous situation. Let her know that whatever she is talking to him about, she can tell you. It is illegal for an older man to date a girl who is 15 – tell her this, he definitely knows this. If she still won't listen to you – you have to let an adult know. She might feel betrayed, but it's better that she is safe. Don't let her meet this guy by herself!