Hi Ruth, welcome.
My husband is the alcoholic addict in my life and his DOC is cocaine too. IMO your husband is an addict. He went down that slippery slope once, crawled out and is on his way back down it again. Welcome to the roller coaster.
All I can say is get yourself all the info you can to help yourself stay sane. Go online and read, read here, go to the bookstore (or library). Read about addiction, read about codependancy and boundaries. A great book I found and have found extreamly useful is Codependant no more. Trust your gut instincts too. Get yourself to an Al-anon or Nar-anon mtg or several.