I'm a bit confused, the title of your thread indicates that his behaviors are a result of previous head traumas, yet, the body of your post seems to point toward a more psychological cause. Has a doctor told him that he has some kind of brain damage that may be attributing to this behavior and symptoms?
If so, he will need to seek help from a multi-disciplinary team that would likely include a neurologist, a psychiatrist, or a specialist who deals with both issues (neuro-psych). With brain injuries, usually there is only so far a person will progress, then they will be left with some level of dysfunction that will be permanent. The brain is a SLOWLY healing organ, so it is not unlikely to see progress over a period of years. Still, it is reasonable to assume if there WAS a cognitive injury, that he will have some limitations to fixing this behavior.
Either way, it's clear you are fearful for him, and I agree you should try to encourage him to get help for himself. That's a bit tricky...because unless you can PROVE he is a danger to himself or others, an involuntary committment will be out of the question. It's not easy (for good reason) to have someone 302'd (involuntarily committed to a psych institution).
If you DO think he is a danger to himself, or others, try to gather the evidence you need to prove that (text messages, voicemails, etc), and proceed by contacting either a psych facility, or the police.
PLEASE be very very very careful here. It sounds like he may be in some ways unstable, and when someone is dealing with any form of psychosis, it adds a great deal of unpredictability to the behavior. If you are EVER fearful around him, YOU get to safety. If he is paranoid, and thinks at ALL you are somehow doing something behind his back, he may become angry. Sadly, it is a fact that people dealing with unstable minds and psychotic thinking can be dangerous, even to those who they cherish the most. Just please be careful, no matter what you decide.
I wish you the best...he clearly needs help. Let's hope with some loving coaxing from you, he'll seek it out on his own. That would be the very best outcome. If he isn't willing, and you feel he is dangerous, you need to consider your options and obligations to pursue an involuntary committment.
Please update us when you can.
If he is being a danger to himself,then i strongly suggest you find him some help whether he wants it or not. It sounds like he is having a very rough time, and i am glad you are trying to figure this out for him!
There was actually a point where i was forced into getting help, and i am thankful for it because i might not be here today. Maybe in the end, he will be thaankful you did the same! He doesnt want these things to happen to him, nobody does! But unfortunately he doesnt seem in the right state of mind to realise how much help he needs. Get him some help!!! Posting here was step one! Good luck to you and your boyfriend!