It's been brought up before as to whether or not ADHD in a relationship should be considered as and treated the same as any other kind of disability. Many have questioned whether it would be a moral failure to leave someone with ADHD since they wouldn't likely leave a spouse who became paralyzed or was stricken with a disease. To me the answer is very tricky. Firstly, no one is suddenly stricken with ADHD as an adult. It is something the person will have been struggling with their whole life whether they were/are aware of it or not. Also, people with ADHD often develop coping mechanisms by adulthood to compensate for a lifetime of inadequacy and shame. These coping mechanisms are usually employed to help mask the disorder and to appear as "normal" whereas with most other diseases or phsyical handicaps this is not possible. This ability to at least in part or for a short period of time mask the ADHD often leaves spouses and partners feeling "duped", and especially so when you throw in the hyperfocus of early courtship that occurs often in ADHD relationships. With individuals having more obvious disabilies there is the opportunity to at least make an informed choice about what a relationship with the person would be like and whether or not you are able to handle it. This is also tricky territory because individuals with ADHD often aren't consiously masking the syptoms intentionally in order to be deceitful, it's more a defense mechanism.
Another reason why it can be a tricky subject is because the symptoms of the disorder can cause some ADHD individuals to behave abusively whether emotionally or physically which is not true about most other diseases and disabilities. This can make the question as to whether or not to stay in a relationship affected by ADHD different than whether to stay in one affected by another disability. Though life can become quite challenging and difficult when a spouse or partner is disabled or becomes so during the course of a relationship, I don't think it should ever be considered a moral failure to abandon an abusive relationship even if it is caused by a disorder. As for the rest? It remains a grey area.