6 years is a long time and he knows what to do to you and your reaction to his abuse and each time you take him back no matter what he has done to you.
You need to leave him and never look back. He will never change and having a terrible childhood gives him no excuse to attack you. It will only get worse, not better.
Do NOT tell you boyfriend what you are doing: Locate a womans abuse shelter / support group (ask the police dept and they can get you in contact with them). They will guide you to what you need to do and how to do it and they will help you. Never feel like you are alone as you are not.
Have you received medical treatment for any of your abuse?