It’s a very personal decision, and there is a lot to consider. Horse back riding is far from the only dangerous sport in the world, and quitting riding is no guarantee you won’t suffer a brain injury some other way. A friend of my mom’s is permanently disabled from a brain injury suffered when he fell off a bicycle (as an adult), something most people would consider pretty damn safe. So it’s a calculated risk that is ultimately up to you. Eventing may be more of a dangerous discipline, but you can fall off at a walk on a ploddy old trail horse and be severely hurt. That is, unfortunately, part of the sport.
I don’t agree with all the people here saying you can be around horses and just not ride, like that is somehow safer. NOPE NOPE NOPE!!! Knock on wood, my most serious injuries have ALWAYS come from on the ground accidents, not falling from horse accidents. Thinking you can protect yourself by not climbing on their backs is faulty logic. In fact, arguably UNLESS you fall off, your head is probably safer ON the horse than around it, because a horse on the ground can knock you down (impact of head off ground), knock you into a wall (impact of head on wall), knock you down and step on you (hoof on head), or kick you (hoof on head). And a lot of people don’t have their helmets on when they are working on the ground with horses (I know I am guilty of this). So if you decide to be around horses still, whether that includes riding or not, being SUPER diligent about helmet use is probably a good idea.
People are making valid points about what you stand to lose, and what your family and loved ones might go through if you suffer another head injury and require care for the rest of your life. Those are totally realistic consequences and shouldn’t be taken lightly. But you could step off the curb tomorrow and get hit by a bus. Any of us could. If it were me, and I say this knowing myself and no one else, I would take extra steps to mitigate the risk (helmets ALL THE TIME, quieter, safer horses, maybe no jumping) but I couldn’t walk away from riding all together. However, you are young and relatively healthy, so this may be the time to go back to school and develop other skills and a new career. If you are working outside horses and riding as a hobby, you will be around horses less (so major risk mitigation there) but you haven’t walked away completely.
Sorry about the situation, it is a crappy choice to have to make, whatever you decide.