How can I convince her he's no good?

So my best friend, whom I love like a sister, is dating this guy, who's a little wierd. He's caused her relationship with her family to become so horrible, (he's trying to make her desert her family and become part of his...they got engaged like two weeks after they started dating), he's caused her to lose all of her friends (she almost lost me), and he's hiding something. He's also caused her to lose everything else (her car, computer, and stuff like that. Everyone knows that he's no good, no matter how many times we tell her this, she believes us, but she always thinks up something to make her change her mind. Well today one her ex's, who was her first love, but they had to break up a few years ago because he moved, now he's back and he's the good guy. How can I convience her that her current boyfriend is no good and that the other guy is? If she dumps the current one, everything will be back to normal, or so I hope.
I can persuade someone to do anything, but this one, I need some adivce before I do what I'm about to do. What do you guys think?

Ok let your friend see what we write on here or similar situations.This guy sounds really messed up.What is t that you are about to do? Hold off I think she's a lil infactuated to be engaged after 2 weeks and this guy has all the signs of being abusive so get her out of there immediatley but don't put yourself in jail over it,                                                                                                                                           Chayla PS:Get the 1st boyfriend to come back around.

Well I'll first ask, are you sure that the first boyfriend still likes her? And second of all, you gotta go to your friend... And it doesn't matter what you do. You have to stop her from dating that guy. I, personally, would slap her in the face. And tell her what he's done. And how much he's taken away from her. And give her evidence of how he doesn't love her. And how he's just using her. The description that you put up about him seems good, repeat that but this time tell HER. And make sure that she cries. Crying= Effect in strategy.

Well I'll first ask, are you sure that the first boyfriend still likes her? And second of all, you gotta go to your friend... And it doesn't matter what you do. You have to stop her from dating that guy. I, personally, would slap her in the face. And tell her what he's done. And how much he's taken away from her. And give her evidence of how he doesn't love her. And how he's just using her. The description that you put up about him seems good, repeat that but this time tell HER. And make sure that she cries. Crying= Effect in strategy.

Tell her what he has been doing. There is really nothing you can do but stick with her. Do you know what he is hiding? If you do tell her, but tell her you aren't trying to break them up you just want to make sure she is safe and doesn't get hurt. Things probably won't go back to normal no matter what happens, but if they do thats very good. I have had this happen to me before, I went out with this guy and I lost everything, just like what you are saying. She most likely won't listen to anyone, but try talking to her. Get her friends and family together where she won't know and invite her and make her listen to everything you all have to say. Tell her that her ex is back and he really loves and misses her. Talk to him, get him to tell her. Try to get him to convince her that he loves her and he wants to be with her. Goodluck, I hope everything works out.