Dog bit my gf

My dog has always been food and toy aggressive but never towards me other than a quick nip. My gf of two years has always been more aggressive towards the dog and has slapped her, yelled at her, and is just otherwise authoritarian. Anyways, my dog was chewing on a paper bag and my dog bit my gf and broke skin. My gf now wants me to get rid of my dog. What do I do.