What do you do when your best mate is a slag and she gets a lovely boy and she if messing him around?

I have a best mate who im EXTREMELY close with, infact inseperable with.. But she is a slag and its embarrasing for me to be with her! She has now fount this lovely boy and he idolises her he wwants a relationship witch is what she needs.. but she is messing him around, in a way i am slightly jealous that she is able to get a lovely boy like that when i get stuck with the fuking druggys, although i do not like the boy my best mate is talking to in anyway but still don't understand how good things come to bad people