You’re understandably shocked and confused right now, but it’s clear what you should do. First, hack into his Facebook account. Then write this as a status: “I am an abusive boyfriend with a tiny weiner. My girlfriend is not a bitch. In fact, it is I who is the bitch. [Insert your name here] is a queen and I don’t deserve her.”
Seriously though, you need to leave him. This is textbook abusive behavior with a modern-day social networking twist. He’s making you humiliate yourself in front of your friends and family. This is abusive, borderline sociopathic behavior. Why do you want to be with a guy who treats you this way? A guy who won’t let you stand up for yourself? First, you need to dump him. Then, you should ask yourself why dumping him wasn’t your first move. Are you attracted to abusive guys? (I’m going to assume this isn’t the first time he’s done something like this. You don’t go from zero to “post on Facebook that you’re my bitch.” He’s probably exhibited abusive behavior in the past.) Are you afraid to leave him? Have you been in this sort of situation with past relationships?
Talk to a friend, parent, relative, therapist, etc. about how you were treated in this relationship. They will help you to see if dating abusive guys is a pattern and to spot the warning signs sooner. No one should treat you this way. You should have been out of the door and out of his life forever the second he pulled the whole “my girlfriend, my bitch” thing. End it now, and talk to someone so the next guy you date doesn’t end up also being an abusive psycho.