hela -
I just want to say how sorry I am you're stuck in such an impossible situation. I applaud your effort to find out about whether a brain injury can cause the things you are witnessing. I wish someone (especially my longtime significant other at the time) would have connected the dots (as you have) and tried to understand. It is horrible how little information patients are given after a head injury that is seemingly mild. I was never told I might experience insomnia, depression, mood swings, anxiety, trouble focusing on simple tasks, personality changes, decision making that was totally out of character, constant confusion... all while not really being able to rationally think through what was going on and connect it to my head injury.
Your post described my life after my head injury. The erratic behavior, the out of the blue decisions that don't fit with the circumstances in your relationship at the time, the emotional roller coaster, the confusion about everything.
I want to let you know that the person you loved is not gone forever... but it is a long road to recovery. Time, routine, reassurance, mental and physical rest, as well as challenging his brain to start to heal (I played games on the Luminosity website and also did neurofeedback/biofeedback for several months which was really helpful). There are things he can do to help speed up his recovery, but ultimately it just takes time, it was probably about 3 years before I was completely "me" again. I don't remember a lot from the years post TBI, they are very jumbled, and I honestly try not to think about them... I lost my long term boyfriend, our two kitties, and the apartment we shared. It is hard to know I was so erratic and broken that my relationship crumbled under the weight. I'm sure, had we both had more information and sought out support from others who have lived through it, we would have had a fighting chance. I hope this helps you in some way. You should prioritize living your life and not let his injury do harm to you both. I think the best thing you can do is try to support him, and give him the tools to understand none of this is his fault. It will not last forever. My heart goes out to you both.
(I'm sorry this is so poorly written... I have a migraine today, so it has been hard to focus enough to write coherently, but I just had to respond because of how much your story echoes parts of my life)