I have to agree with Trevor. I could understand using that excuse with maybe a one night stand (sexy right? Lol) but with someone you care about and are expecting a long term relationship with, it would be a good idea to start off the relationship being completely honest. Now, with that said, many of us wait a good while before we build up the courage to actually tell, and that's usually a good route to go as you can gain a foundation of trust in the relationship which helps.
If you're serious and really looking to make this an ongoing thing, I wouldn't lie to him, he's gonna figure it out at some point. So, if you're really that adamant about wearing diapers to bed every night, I'd start out by telling him the truth right off the bat. Just my $.02
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