As long as you are engaging with him, you cannot really begin to heal. The band aid gets ripped off constantly.
He is determined to stay, and you are afraid to see him go I think.
It is also normal to feel heavy sadness at the end of a 20 year "big love" but he has chosen drinking over the relationship over and over.
You really need to stop trying to "understand" his motivations, words, or actions at this point and take care of you.
You can let go with love, but most importantly you need to let go and love yourself.