Well, what a very juicy question.... with several drops of blood per gallon I may add...
The answer is: there is no single answer. My personal take is that your H is not going to want to be back in the old M any more than you do (I know my H does not), and he is going to be willing to cooperate.
The catch is, of course, he is going to do it HIS way, not yours. And he would probably resent any ultimatums or orders.
So, what to do? What I am planning on doing is talking, a lot, but most importantly doing twice as much listening. Your H is a grown up man and will hopefully find a way to change.
When he decides to come back, talk to him and explain your fears. Do not judge him and do not diagnose him, and do not volunteer solutions. Just make it YOUR problem, as in: "I am concerned about how we manage stress and I fear that if we go back together we can backslide. How do you think we can do to avoid it..? That type of thing
"You don't throw a whole life away just 'cause it's banged up a little"
Tom Smith in "Seabiscuit"