Another thread got me thinking about this. And for me it wasn't any of the times he beat me and was arrested, nor the times friends drove over to 'rescue' me.
It took a very long time and my final realisation was when he came home from work hammered at 11pm, with fish and chips for himself, knowing I had been stuck in all day hungry and without any money. He wolfed it down and kept nodding to an empty glass on the table, I realised he meant I should go get him water and almost did as I normally would. But then stopped myself. That was it.