Before I get into any of this reply, I just want to say that if this isn't a LARP, you need to talk to your boyfriend. ABDL can be extremely varied and the very fundamental roots can be hugely different person to person. For example, for me, I really like the spanking connection, but it turns out most ABDLs aren't into spanking! For some people they like messing, but more than half of ABDLs don't.
>What does being a little mean
In its broadest sense, taking on the imagined role of someone dependent, needy, to be doted on/cared for
>What does he want to do with me
Only he can answer this. It sounds like he probably at least wants you to play along with babying a bit.
>What does he want me to do
Most likely? Say you accept him. Reassure him that you are not disgusted by him.
>Do I have to wear diapers?
You don't have to do anything you don't want to. You've made it a year without putting on diapers. You're going to have to ask him though - if you indulge him in other ways like a sippy cup or watching cartoons together, will that be enough? I am guessing he'll take what he can get.
I would also say that you shouldn't feel overly anxious about wearing diapers though. Really, as long as you aren't using them at all they're just like scandalous panties. Like imagine your boyfriend asked you to wear some of those edible chocolate panties or something crotchless. Risque but just clothing. That's what diapers are. I agree fully that USING IT is a whole different threshold of course.