Hi Yuki. Are you Japanese? Just asking because I spent 8 years in Japan, so speak fairly fluently.
It depends on what type of person you're boyfriend is. If it was me, I would want you to be completely honest with me, and I wouldn't care if you said you had to wear diapers. I\d be quite turned on, in fact. ()
If he's squeemish though, or you think he might ridicule you for it... well, perhaps he's not the right guy for you? I would keep it secret until you're sure what kind of person he is, and don't sleep with him.