You have to go to the police and make a formal complaint against him.
Tell them everything, do not worry about 'my word against his', many complaints are like that. He has been arrested for GBH so there is confimation of his violence. Report this to the police, if possible the same police station that charged him with GBH. If that is not possible make sure the police you talk to are aware that he has a GBH prosecution pending.
You need to get an injunction against him so that he can not contact you, the police will help with that.