I am glad that you knew you could return and find a welcome and understanding.
You have something that most CGs do not have when they find themselves up the creek without a paddle – you already have a paddle and you know how to row for shore.  
In ‘My Journal’ (which is our CG forum), Kathryn’s thread entitled ‘Believe’ has expressed her concern about her husband’s gambling in recent months.   She is gamble-free and has been so for a few years and her thread is inspirational to many.   I think it would be good for you to read and I know she would reply to you if you posted on her thread.
Please do not think I am judgemental when I say that I will never gamble in any way again as a result of the addiction to gamble being in my life.  My CG who is gamble-free has told me that he has no problem with me gambling but he knows he cannot.   The choice I have made is mine and because of this I have avoided the ‘possibility’ of being caught.
Before anybody jumps on me and says this couldn’t happen to me, my answer is that I don’t know why it happened to my CG and I don’t know why it didn’t happen to me – but it is a fact that the addiction was there for him but not for me.  
I am aware having talked to many CGs over the years about the attraction of lights, noise and energy.   As a non-CG I don’t fully understand but what I do know is that all these ‘tricks’ to entice are designed by clever corporations to entice people to part with their money and the potential CG is an unfortunate pawn.  
Gambling is as old as the hills – it will not go away.   You are completely correct when you recognise that it is you that has to walk away and more importantly, stay away.   In this forum we come to realise that the addiction to gamble is not just about loss of money – in fact that becomes the least part.   It is what it does to the mind of a loved one that hurts – it is the lack of empathy and the lies which stem from guilt and misery.  
This addiction has taken your marriage away from you and I think that is quite enough.   I believe that F&F and CGs are not on different sides but are the other half of the same addiction because without enablement it starves.    Like all CGs you have found out the hard way that gambling is not something that you can do recreationally – it is poison to you.    In my opinion there is no responsible gambling for a CG – this site believes in abstention being the way forward. 
I think your username is now sadly more apt than it was before.   I urge you to walk away, to join GA, to read Kathryn’s thread, to join our community groups where you can talk to other CGs.   Have you said out loud yet ‘I am RTWA and I am a compulsive gambler’ – sometimes it shocks to hear it even when you know. 
You were never going to change your ex-husband by threatening him; you are never going to make a scrap of difference to him by joining him in his addiction.  Turning your life around and living gamble-free, I believe, is the finest way you can show him how to live and it sure as **** is the finest way for you to live.  You do deserve better.  Get off the roller-coaster now for both your sakes.
Well done on coming back – I wish you well and I hope for an update soon that you are living in control of your life again.   You are able to see this addiction from both halves – use that knowledge to help others and make something good come out of the horrendous experience you have had.