sorry hk that you are having trouble, i know its sounds all so overwhelming, but it does get better. first, try to take some deep breathes, then its time to find something that you may like to do, to keep your mind occupied. do what ever you can to block out those negative obssessive thoughts, change them as they come to mind into positive ones. praying, reading out loud to myself, singing my favorite song, or cleaning closets, use to help me to keep my mind busy in stead of allowing those thoughts to invade my thinking.
try not to worry, its common to have those thoughts. it takes time and a little practice, but it does get better. alanon and naranon, meetings for families of the addicted, helps a lot too. maybe you can search your area for one or two. have you read the stickies at the top of the forum, good info there too.
your husband is in a good place, no need to trouble yourself just yet about what he may do later, right now, he's probably too busy trying to figure out how to not use drugs and hopefully learning valuable tools that he will need to keep it up. try not to look so far into the future, try to stay focused on this day, and let tomorrow take care of it self. one day at a time, you will get through this.
boundaries are just decision you make for yourself about what you are willing to live with concerning his addictive behavior. keeping you and your husband in my prayers.