I suspect my husband has ADD but he is in denial

Does anyone have any advice on how I can help my husband see the ADD signs that I can see he displays? We have a 19 year old son who was diagnosed ADHD when he was 5 (so I understand ADHD challenges). My husband had no issues excepting our son's diagnosis. But when I bring up the topic that he may have it too, he brushes it off as a non-issue. I believe it is the reason for several of our marital issues like, arguing & financial problems. He has a business but hasn't been paid in a year because of poor decisions years ago.  We have had issues for years and now I am fighting off anger and resentment towards him daily. Not sure how much more I can take. Relationships require work and I feel like I'm the only one working at it. I could really use some advise from those who can relate to my situation. Thanks