I haven't experienced any significant personality shifts from my injury itself but from chatting to others in my support group it's pretty common. And my medical team listed irritability, lack of impulse control, depression and apathy as possible symptoms that people might encounter as a result of the injury, let alone the emotions you deal with as a result of coming to terms with a long term condition. Please don't hate yourself for decisions made back then. You did what you could to the best of your ability, with the knowledge and support that you had at the time. People do a lot of dumb stuff independent of having a brain injury. Cut yourself some slack, it's not easy to navigate life at the best of times it's a lot harder when your central command is jostled.

The one thing I've noticed personally is that people don't really understand when you talk about brain injury. It doesn't surprise me that your personality changes were dismissed as unrelated. When I describe my symptoms to friends and family they are totally baffled and don't seem to understand the severity and the implications. Even many of the medical professionals don't quite get it. Until you've had a lingering concussion and felt the weight of the symptoms following you day in and day out, you just can't know what it's like. If you can, see if there's a support group in your area. It's been so valuable to me to chat with others on coping strategies, to laugh about our common issues, and to shed a few tears if needed.

I flip back and forth between this subreddit and r/tbi which you may find useful as well.