You just need to remember that relationships are two sided. Personally, I'd say if he can't get off with out diapers, then he probably needs to change something. I don't think that's too fair to you to be restricted to his sexual needs. I'm sure that you are a sweet heart, I can tell that just by the fact that you care. But, if I was you, I wouldn't induldge your boyfriend with diapers until he's able to be more responsive to vanilla sex or what ever y'all do. (You really should just jump him sometime when he's got no time to think, think super heat of the moment amazing movie sex. He'll be too flustered to think about anything but you.)
Lol, now down to business .
Not all diapers are all covered in plastic or have the plastic-y smell or look too much like diapers. If he'll fit or you will fit, or whatever you want, Goodnights or Underjams are made to be as underwear non-diaperish as possible. "Normal" ( ) pre-teens and teenagers that wet the bed probably hate diapers as much or more than you. They are pull-ups, but about the most non-diaper diaper that you can find, I'd say. There are lots of underwear like pull ups for adults too, I think depends and tena are the most common that don't need to be ordered on the internets. (FYI Depends suck) That might be a starting point for you to ease into it.
But first, you need to bring that boy down a notch to where you're comfortable. I'm sure it's awesome between you two right now, and it'll keep getting better as long as he's willing to make you happy and you stay as open minded as you sound.