Hello, and welcome! The most important thing you've got down and that's accepting him and being willing to learn, so you'll definitely do fine
I think you need to get him to sit down and figure out what he likes about being little. Maybe create like a list of things he'd like you to do as a Mommy and what kind of expectations he has. I know you said he's unsure how to explain it, but I think it's important he sits down and figures these things out. You could also do the same and figure out what you are okay with and what your expectations of him might be.
As for you learning about this lifestyle, the roles, and just what it is, I've found that this site has some great articles to read through. If you go to the top of the page and click on "Resources" then click on "Educational Articles" you'll find lots to get you started. Or this link takes you to the same place: viewforum.php?f=88
It may be beneficial for your boyfriend to read through some of the articles as well. They may give him a better idea of what he is looking for and what he wants.
I wish you both good luck and happy times!