ML, you poor woman. Im so sorry.
Gambling, sex and alcohol all go together as a group of 'up' type activities/compulsions. He uses them to feel better about himself. He is after the 'rush' or the feeling of being 'high'. He then crashes the next day and feels wretched. With some, drugs, work or even romantic love are involved as compulsions as well. Anyway, most people like him have more than one of the activities in the mix. They often blame one activity for the other, but really they are just separate and additions compulsions which dull the same original pain, often stemming from their childhood experiences.
So he has two alternatives. One is to blame himself and take responsibility and the other is to blame you. He sees that the latter is easier, and he doesnt want to take responsibility anyway, as it means changes to his life which he is not prepared to make.
This is then further complicated by the inevitable internal dynamics of a relationship over time, where both of you in some way come to see the relationship issues as part of the problem, whereas they are just symptoms of the original problems above. 'Rushes' of romance or feeling can sometimes get involved too, in the feelings engendered by repeated break ups and new beginnings. The relationship itself becomes a cycle of highs and lows.
In this scenario the partner, ie yourself, usually has some issues in their own past which they are also trying to fix, and which leads to a need to try to fix others, and to accept what most people would not. They may themselves have a past story relating to feelings of unworthiness or neglect or feeling unloved, ie some past trauma. So they try within the current relationship to fix things, when they are really trying to fix their original problem too.
I say this because if you can get to the bottom of why you have been willing to continue to trust him and accept this treatment, you are half way to truly protecting yourself from doing it, and he will lose any unhealthy power he has over you. It will also protect you in future relationships- think how many people go from one difficult relationship to another, without meaning to.
You do know on the face of it that he is not fixable, but you need to organically and long term believe it.
Take care. And I hope you find the strength to get him out of your house and hopefully your life.