Should i threaten the guy thats been hurting my best friend?

I'd say talk to the girlfriend...but then again if you talk to the girlfriend ad it leads them to breakup then he will go crying to your friend and your friend will obviously take him. ANd then what if he blames her for him and his gf's boyfriend? Try to get your friend to meet new guys nd possibility if you can get a guy to text him to sty the F away from her.