suncatcher, I know from experience that detaching from your own child is tremendously painful and usually produces feelings of great guilt in the parent.
As for your immediate question---I would suggest that you step back (detach ) from it---because it is in your Ex-husband's home. He is responsible for the handling the rules of the home--who stays; who contributes & how much, etc.
In general, I would say to you to learn as much about this disease (I assume that he is drinking very heavily--no?) as you possibly can. Knowledge is power. He is a fairly young adult---and he needs to learn the rules of adult living and responsibility----and, trust me--the universe will give him feed back on this. It is important that you resist the mother's impulse to give comfort and soften his landings. He must feel the consequences of his own actions (or inactions...LOL). Do not try to buffer his pain in this regard.
This does not mean that you don't love him. You will always love him. Don't worry if he gets mad at you or "blames" you or reacts in negative ways toward you. He will always love you--I promise. Sometimes, the maturation process is very long and drawn out. The best way for this to happen is for him to have to stand on his own two feet. He will become very resourceful if he HAS to. Don't worry if he has to live under a bridge or go to a shelter---if it ever gets that bad. That will teach him much more that sl eeping on your couch and giving you a nervous break-down ever will.
I don't know if you and your ex have a good relationship or not. It is so important for you to get some support--because is more likely a marathon than a sprint. Alanon can do that for you---isolation makes it so much worse to bear. It might help if you and your ex attended alanon together--if that is possible.
Continue to learn and talk to other parents that have gone this road. Also talk to long-recovered alcoholics---they can give you some very good advice---because they know what they are talking about.
Sometimes, that right thing for a parent to do is the hardest thing. Please post here anythime you need to. There are some others who have had to deal with their adult children, also.
sincerely,
dandylion