Thank you for your question and welcome to ADHDCentral. I applaud you for wanting to understand more about your husband's ADHD.
From your question it is difficult to know exactly what is causing his lack of desire. Have you discussed your concerns with your husband? Does he know that you are unhappy with this aspect of your relationship? Sexual desire is different for each person, where one person may want sex on a daily basis, other people may be happy with more infrequent sex. All of this is normal, there is no "right" or "wrong" to how often a married couple should engage in sexual activity. However, it is important for married couples to communicate their needs and desires and certainly it is preferable that the couple find a way to satisfy both people.
You also indicated your husband does not take medication for his ADHD, but you do not indicate whether he is receiving any type of treatment or if he just manages his ADHD on his own, without the help of a medical professional.
The first place to start would be with your husband's doctor to make sure there is no physical condition preventing him from having or enjoying sexual relations. Once this is done, you can try to find the reason for his lack of desire or interest. ADHD itself is not necessarily a reason for lack of desire, but there are sometimes underlying factors that may be going on.
Hypersensitivity is common in people with ADHD and there may be a problem with feeling uncomfortable being touched. Physical closeness and touch can cause feelings of being overwhelmed. An article on the site explains this in more detail:
Managing Hypersensitivities in Adults with ADHD
There is also a high incident rate of depression in adults (and children) with ADHD. Although we often associate depression with someone who has no interest in activities at all, that is not always the case. Mild depression can be masked by years of trying to hide the depression or simply of not understanding it. Depression can certainly inhibit someone's desire for sex.
ADHD and Depression
I think it would be a good idea to talk with your husband about this issue and let him know how important it is to you. Finding out if there is something going on that is preventing him from enjoying this intimacy and important part of your relationship is the first step.
I hope this information helps.