He may be angry because he's finally feeling the consequences of his drinking - his marriage is over and he's being "abandoned" by you. My ex became even angrier and more vindictive during the divorce process, which I didn't understand for a while - I thought "this is what you wanted - you made it clear you don't like being married to me, so why all the bellowing and snorting when you're finally getting unmarried?". It was explained to me that abandonment fears are not logical - even though ex had spent years telling me how unimportant and insignificant I was, he was still angry (and a bit frightened) when I changed things by moving out.
For this weekend, in similar situations one thing that helped me was visualization exercises - can you imagine your ex as a tree? Just a big tall thing with branches that sometimes blow in the wind and sometimes branches fall off (or acorns, pinecones, whatever). A tree has no inner life or emotions, so there's no point wondering "What is the tree feeling that is causing its acorns to fall off? Is the tree upset and that's why its leaves are changing color?". You can't "understand" a tree because there's nothing to understand.
I'm not saying your ex is like a tree in that he has no inner life, but if you treat him as if he was like a tree and just go about your business and let him do whatever he's going to do without engaging, you may have more inner peace.