With a verbal abuser? or in general?
Verbal abuse- Anyone who verbally abuses has a potential to turn physically violent, don't just break up, make sure you have someone with you, kinda discretely, and state why you are and give them the whole truth, and then say, 'and that's why I want to break up.' and if it turns violent, tell someone right away, and that's when your friend comes in handy.
General- same thing, you can drop the friend being a ninja thing, but if it's more comfortable than bring them, don't be afraid and chicken out, because if you do, it means the longer your with them, which means more misery.
i will be making an article tonight hopefully about this in fuller detail :D