My best friend ditched me for her boyfriend, what should I do?

My best friend and I have been best friends for 5years she got a boyfriend once, and ditched me for him. He called me names and all kinds of rude things I shrugged it off, but my best friend and I didn't speak for a long time. When they broke up I got her back as my friend, but now she has a new boyfriend, and she's ditched me for him. Her boyfriend is now harassing me, threatening me, and calling me names. He had called her uninteresting and all kinds of things. They almost broke up because of this, but didn't. I'm worried he's emotionally abusing her and she can't get out of the relationship. I don't know what to do, I don't want to see her in such a mess. Her boyfriend ruined our friendship. Help?! :(