What is the best way to tell someone im dating that I wear diapers due to my disability?

Be honest/open. Once comfortable and able to talk like friends, then discuss health issues or your disability. Next, say you have a concern about yourself that you want them to be aware of. You can say your disability causes you to feel embarrassed because you use diapers. Maybe state this while giving them a big hug and whisper it in their ear. Then possibly try to have a laugh. Humor can help with stress.