When you ingest a drug daily it changes your body chemistry, whether the drug is caffeine, nicotine, antidepressants or alcohol. I've observed personality and cognitive changes in my AH that, coincidentally, has emerged and gotten more pronounced as he has descended further into alcohol abuse. It took me a long time to connect the two but now that I have, I can see that the increasingly offensive and annoying behavior was at least in part due to his substance abuse (and perhaps the rest was just him turning into a real *******, who knows).
I find it helpful to sit and think about it all and try to sort it out in my head, but at a certain point beware of sliding down into that dark hole, because in the end not much makes real sense. Sometimes you just have to shrug and move along.