I’m sorry for what you are going through. My husband and son both have ADHD and it is difficult to live with.
I have some advice for you to avoid going crazy – research ADD/ADHD and learn everything you can. Understanding that your husband’s brain works differently and processes information differently as well will be very helpful. I was miserable until I learned what is related to ADD/ADHD and what is simply behavioral that he can change. The other piece of advice is to talk to him when he is in a mood to listen, or even if he’s not. Tell him he needs to get to the doctor and go on medication immediately and that he also needs to learn all about it. Individual Counseling for both of you would help as well.
I assume you don’t have kids? If it’s just the two of you then if he isn’t willing to do what is necessary for his and your emotional and mental health, then you can decide if you wish to stay with someone who won’t do anything about himself.
Best wishes to you both.