As usual, those believing in tough love are out in full force, because of course they've never needed advice with compassion in all their lives! They were hatched as perfect nurses. Let me offer a different perspective. First, relax. You have failed no one. You have a medical issue, one that is going to make school a lot harder. But you can get through. I also was diagnosed with ADHD as an adult. I'm in grad school now, and it is tough, but manageable. Ignore all the people who say,"but so-and-so did it, why can't you?" everyone is different. Find out what works for you. If you do take meds, work closely with your provider to titrate for max effect. Consider getting an ADHD coach to help you when you start in the program again. I think that it is great that your were an advocate for your class; we need those types in nursing. However, remember your education comes first. You have to take care of you!
I'm also wondering why they did not offer accommodations if you have ADHD documented. Under Title IX (federal law) disabled students have certain rights. Every university has a Title IX compliance officer. I suggest you get in touch with yours. Your school may not have deprived you of your rights, but I would certainly check. Read more about it here: Students with Disabilities Preparing for Postsecondary Education
Keep your chin up and work hard. Good Luck!