untreated ADHD

My husband has never been treated for his ADHD. There for he never writes anything down and consequently never remembers anything. He is not willing to try. When he is questioned he just remains silent or becomes aggressive. What am I meant to do? I am in a wheelchair you have no choice but to book transport 24 hours in advance you cannot wait til the day and decide to travel. You have to plan in advance. This seems impossible for my husband. I know it untreated ADHD but how can I cope with his spontaneous if the world want wheelchairs to book in advance?!