Hi nnfc
I have loved and hated too and I can’t explain how it works. I think when a question keeps returning with no answer it is best to put it on a back-burner until you are ready – and you will be. 
Self-deprecation is common and used by CGs as an effective form of manipulation.   It is important, in my opinion, not to feel pity or join in with such a conversation..  
I think if it was me, maybe I would say something like ‘if that is how you feel there is little point in talking about it’ and walk away the reason being because there is little point in talking about it.   He is right – he can’t be trusted, he is wrong – he can change, he is wrong – he is not a bad person.
Stuck on the wall beside me is the quote ‘I have often regretted my speech, never my silence’. Some people have found it helps and maybe it is the ‘something different’ you could try.   I would imagine you tried to make him feel better when he was seeking pity but if you did you could not succeed.   He could hear the words but not the meaning because his addiction was between you.
You don’t have to explain the difference between a CG throwing the family’s money away when there is surplus and throwing it away when there is debt. The addiction to gamble unfortunately gets worse unless it is treated and it is the behaviour that goes with it that is unacceptable too. 
Have you spoken to any of your children about their father’s gambling?
I am sorry it has been a time since I spoke to you – the forum is busy these days and there are not enough hours in the days sometimes.    You are on our radar though and you would be welcome in a Friends and Family group at any time – nothing said in the group appears on the forum.
Hoping to hear