I was in a car accident a couple years ago and suffered brain damage, it is mild but still present and there are mental changes. With that being said, you have choices, you can either change with them, decide if the different person they have become is still the one for you or you can decide to just be friends and support them from a distance. When something happens to change a person, they cannot usually control who they will become. It is an ongoing learning process for both people involved. I am still me, but different. There are similarities in my learned actions, the instinctual actions are the same. My personality is more fragile in some areas and stronger in others, there are many things I do not remember. The trauma is different for everyone, but without a scenario it is hard to advise someone. Hope this gives an insight, but I need more details to actually try to help or advise you. Good luck and hope it works out!!