Hi, GillianGillian. I am sorry this is happening to you!
I also hit the left side of my head (all three times actually) and notice that i am more "emotionally charged." I wish that I had some advice for you, but I can only hope that you find some peace in the fact that someone else is going through similar things.
I too, have been good friends with someone, and we had been dating for a while, but my whole take on our situation has changed (since my most recent injury), and I argue with him a lot more, and feel as though I am being cheated in this whole relationship. (not quite the same, but a sudden shift in my feelings about him seems to parallel a bit with your situation)
I, however, remember what has happened each time. I don't know if this has helped you at all since I don't have any words of wisdom.
But I understand to a degree. Hope there are some answers out there!