oh brother, this is gonna be troublesome. So, ready to begin?
The modus operandum is simple: tell her it is over (RECORD THIS CONVERSATION). Cut contact - ALL CONTACT! and that's it. Don't try to be friends, don't try to keep something going on, if it's over, then it's over. No point in keeping her around if she's that soul sucking of a girlfriend.

Now, there are several things you need to keep in mind. Are you living together? Are there things of yours at her place or vice-versa that you'd like retrieved? Are there friends in common, or do you still kept in touch with your own friends?

Living together will make this whole process much harder, but get packing and securing your things.
Talk to your friends. Don't speak ill of her to them, there's no need to be badmouthing her on her back. The relationship is over, it was not working for you. and that's all you need to say. Keep your friends close, they should help you in dealing with any negative feelings.

Make a plan for yourself. What do you want out of life? What are your goals? Write them down and prepare a plan to make them happen!
Go to gym, start lifting. The iron temple demands dedication and discipline, both are needed to accomplish your goals, and starting with your physique is the easiest one.

Good luck on the path, brother.