Yes this seems to be common. In other relationships it is the loss of the connection but in the case of A's, it is that PLUS knowing that a person is slowly killing themselves and destroying good things in their life.
That is the part that I don't think ever gives a person closure. It is hard to watch or know that is going on when you care about them. But it is ok to not have closure. You make peace with it, it is about acceptance and not feeling you are responsible for his choices, or his family's denial.
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