"I was thinking about temporarily (1 -2 months) moving out - to give me some time to work on myself and see if he wants to work on himself. Then I/ we can reevaluate the situation (if he is seeking treatment then we could start working on our marriage, if not I would need to move on). Do you think that is a realistic plan or does this usually not work?"
I think the 1-2 month separation is a good idea. It would give you the time you need to reevaluate, to live without the drama, to channel your energy into yourself and your own projects. You would have to be strong to focus on yourself during this time. You would have to make it clear to him that you are doing this for you--and not because you are trying to get him to change.
Does it usually not work? That depends what you are asking. If you are asking whether or not you will find peace and happiness within yourself? I would wager that you will feel a lot better not living with him. If you are asking whether or not he will he start seeking treatment? Maybe... maybe not. All addicts are different and have different bottoms. Whatever decision you make, you need to do it regardless of the outcome. Would you move out for 1-2 months knowing he will not change, but you would?