Some good suggestions above. Here are my additions.
The passage of time is a mystery. There is only now or later. If you care about him being on time, send him reminders (put events on the calendar, outright nag, and do not answer the question “What time is it?” with an actual time — say, for example, “It’s time to get dressed.”).
The best you can hope for organization is that he can find his keys each morning, the driving license is in his pocket, the car rarely runs out of gas in a weird place, and the taxes are up to date. Everything else chances are you’ll have to deal with, if it bother you.
He may have trouble starting or finishing things for no apparent reason. There is no point in psychoanalyzing him. If you want to help, suggest the next small action he can do to move things forward, if you can see one.
As Anne said, inability to improve behaviour is one thing, denial and unacknowledged jerky behaviour is something else. There is no excuse for that.
DH and I both have ADHD (only figured it out because our daughter got diagnosed), and we’ve been together for more than 20 years. The main thing is to focus on solving the problem, not improving the person. Oh, and the judicious application of nagging (aka repeated reminders), on both sides 🙂