Sorry to ask - you didn't have a thread some time ago about your DP's apparent change in personality after the head injury, did you?
Not that it matters, because as others have said, he's an adult, and even if his changes are to do with his head injury, it's up to him to do something about it.
I think some of the things you wrote in your other thread, that he has said to you, show that he is happy to verbally abuse you as well. It might be learnt from his mother, rather than innate - but given that he has suffered from her abuse all his life, you would think that he wouldn't want to inflict that on you, the woman he supposedly loves.
In the end, he might love you but it's clear that he doesn't love you enough - and his opinion of you and respect for you is insufficient for a decent partnership between you.
I'm sorry for the pain you're going through just now but can't help but agree with the PP who said that it's better than going through FAR MORE pain later down the line, possibly with children thrown into the mix.
Get away from this one and learn from it - especially that love doesn't cure everything, sometimes the lovee has to actually do something proactive to help themselves too. You couldn't love him any more, there is nothing you can do to help him. Remember the 3 Cs (they're probably here already but still):
You did not Cause this
You cannot Control this
You cannot Cure this.
It's his problem to deal with; it will only be your problem if you go back to him and allow him to continue to treat you with insufficient human decency - so stay strong and stay away. xxx