Should I send this guy a message on facebook?

Ok so me and my friend are in 7th grade and we met a sophomore a few months back, he seemed nice and all but he smoked weed and stuff like that. My friend loves boys like that for some reason. Everyone tried to talk her out of it and shes gotten better but you can tell shes not going to change. I made her promise not to see that guy or talk to him and she didn’t for a while but now all she talks about at school is him and usually there’s a lot of cussing and such. She turned everyone in our grade against him and for the most part no one really liked him in the first place. Shes gets very angry whenever someone brings up his name. But won’t tell me or anyone else for that matter why. What should I do? Hes on facebook should I send him a message or something? Hes got to know why shes like this. Thanks.