I think you did absolutely great.   You didn’t allow his addiction to pull the strings.   You didn’t chase after him and plead.   You were cool.  
Keep it going – mean what you say and know that you mean it.   Try not to backslide because he only has to see the green light once.   
Forcing GA is not ideal but along with all the other things you are doing I cannot fault your actions.   It was great to hear that once he has gone he felt better for going.    You are not frog-marching him to the meetings – you are giving serious ultimatums and you mean them.  It is the knowledge that you mean them that puts you in control.
You have started a different ball rolling and you are controlling it – you are making a difference.     It stems from your confidence and your self-belief – they are powerful things and they are the things that are lost when the addiction takes control.
Nobody can predict an outcome with a CG but once you started putting your boundaries up you gave your CG’s addiction a kick.   Your CG knows now that you are not in the enablement game – that you are not going to play, which hopefully will give him the push into a true recovery that he will not only keep his relationship alive but will bring him peace of mind and a gamble-free life.  
I am hopefully getting over a virus that has knocked the stuffing out of me over the past few days but I will look for further updates from you.
Well done