Honestly, I could never let it go while I was living with him. And even for quite a while after he left I still had some major anger. It took me a really long time and a lot of space to work through all that. Not surprising, considering it was twenty years in the making. The thing is, most people just want to "get rid" of anger because they think it's bad, or because it feels uncomfortable. But, anger is a sign. It's an emotion that lets us know something is wrong, something needs to change. You cannot really get rid of the anger without addressing its cause.
Having said all that, the best tool I found for dealing with anger was journaling. I could use ALL CAPS and lots of !!!!!!!!!! and double and triple underlines and just get it all out there on the page. In fact, I labeled my notebook that I used "Book of Anger," lol.
L