Probably the best thing you can do is set him at ease about it. Many of us have held these secret desires since we were kids, and it's hard opening the door to let someone in. A LOT depends on (sorry about that...) your guy. Some crave a mommy, but how many women, in their right minds, want to play mommy/child for 50 years? If he's AB, chances are he'll be oriented that way, but, if he's smart, he'll realize he's lucky to have a partner WILLING to PLAY, as long as the work is done, the kids are fed, the mortgage is paid, and the cars are cleaned. Obviously, some AB's don't get it...
If he's DL, then it'll be more about wearing, and using, but not so much about baby items, although some (myself included) have fantasies about forced regression. Sometimes just the wearing takes care of the need, but more likely there'll probably still be a need to visit sites, view pictures, read others experiences, etc. The brave do munches, and get together with other ABDL's, but that's not a requirement to be happy, just icing on the cake.
Obviously, communication is the key. Non-judgemental communication. Tell him your fantasies, too! You're as big of a part in the relationship as he is, so SHARE your deepest desires, then lay out a plan to fulfill each other's dreams. Intuition is important, too. Knowing what's working, and what's not, and being willing to be flexible enough to keep things positive.
Also, let him explain what it all means to him, and what he THINKS he needs from you. This will certainly change & evolve over time. Don't think just because things are changing, you're doing something wrong. We honestly do evolve, as we find someone to share this with. What once was super secret, now evolves into a lifestyle arrangement that can last for decades. Try not to push so hard to "understand" everything, because very likely he doesn't quite understand himself fully. We're all in this sort of conflict over whether to be adult-like or child-like, because the clothing tends towards the child, but we can't escape our adult-sized bodies, and all of the adult problems in life.
Hope this helps. Been married 28 years, but have lived with my infantilism since I was a toddler. I always hoped it would just go away, but the needs & desires only grew stronger, the older I got, eventually merging with my sexuality, to become the adult me. I married a wonderful vanilla that might have initially thought marriage would eliminate the diaper desires, but they just morphed into something slightly different, and we adjusted, and learned how to cope. Now I wear freely, and she doesn't worry that I'll turn into a diapered baby, but, instead, I'm just a calmer, more understanding diapered husband, father, grandfather, uncle, etc. You can make this work! I wish you well!
JamieBoy