Hello,
i am a DL/AB as my name implies this is a secret life. What you need to be asking yourself, how far am i willing to go? If i bring this up, how mush support can i give him? Im i willing to participate or just let him do what he wants but don't involve me. I do not know what his "thing" is with diapers, but i can tell you, if my wife at the time when she saw my stash had been more open to them and was willing to participate rather then humiliate and belittle me because of my fetish, i would have been very happy. If you love him and can be the type of person that can explore this kinky side of his then do not be afraid to bring it up. he will be embarrassed at first but after he sees that you want to share this with him and experience what it is about he will be very happy and love you even more. How you go about it is up to you.