I learned a lot about anger with grief recovery work.
Five stages: denial, bargaining, anger, depression and acceptance.
They are all part of the grief process (for death, for divorce, for not having needs met etc).
I am coming up on two years separated. I have been through the process once (w/out acceptance), I am working through it again without denial. Learning that the emotions from this were normal, and that if I choose to "stuff" them down I was only going to drag them out even further.
There is a big difference from anger when you are working on your recovery and unresolved anger that is never looked at. Just the fact that you posted here means you are working on it.
Also there are positives in FEELING anger, it is how we choose to ACT on it that can get us into trouble. When I saw that anger helped me to set boundaries, not get taken advantage of and get things MOVING it actually was a good thing. I suspect there is some of that for you also.
Finally when I beat myself up about the anger I just made myself feel worse...and more stuck.
In affair work they say it takes 2-5 years to heal from it. I have found it to be true in terms of time. I have not seen data on time for healing with addiction in the family.....but I do know that at three months I was still really struggling with shock, denial etc.