I believe that in some cases, it's not that the person with ADHD is incapable of changing. I believe they don't change because things work better for them the way they are. They are simply unwilling to change. Why would they want to change when they get their way most of the time and they have someone who is willing to do all the little things in a marriage / relationship that they themselves don't want to do?
My partner has ADHD and we are not married. We don't live together because I have a daughter 15 who is still in high school. I cannot move in with him yet, because I would have to drive her from where he lives to where my daughter goes to school and I currently live. For me driving her back and forth on the weeks that I have her would be too stressful. I work full-time and I go to school part-time.
I am 53, and my boyfriend is 51. He was diagnosed with ADHD years before I met him. He has had two failed marriages and other failed relationships with women partly as a result of his ADHD not being treated properly. He is not medicated, because he didn't like the way that he felt while he was on medication. His ex-wife liked him on medication because then she didn't have to deal with his exuberance and hyperactivity. After years of struggling in his life with lack of organization, lack of focus, and financial problems, he decided to go to a behavioral therapist.
The therapist helped him create routines and he is very particular about sticking to them. He does the same things in the same order every morning before going to work. It has saved him financially. In his daily life he keeps a very neat house and is on top of every penny he spends. Because he is a computer geek he has everything organized on his computer including a spreadsheet where he tracks his money. (He can tell me exactly how much he spent in gas over the last 5 years.) Some people might think it's a bit extreme but it works for him.
He does these things because he was tired of living his life the way he was. He made that choice to do better and did it without medication. He has had problems in the past with over self-medicating with marijuana but he is looking for other ways to deal with ADHD issues and chronic problems with his back.
I don't know what life will be like once we are married and living together. I hope it will be much like it is now when I stay with him every other week when my daughter is at her father's house.
I don't have half the problems with my boyfriend that I did with my ex-husband who was controlling, narcissistic and abusive. I believe we all make choices in life and ADHD or not you can choose differently.
I'd like to add to the end of this post that I realize there are variations with ADHD. Some cases may be more severe than others.