ArchieRoni said:
It can be something that a lot of people feel guilty about, and it can be something that they keep secret enough that they can't think of the words to even bring it up. So, even though you've been together for 8 years, there are a lot of pretty good reasons why he might never have told you up to this point. It will help him a lot if you can be understanding and don't treat his embarrassment and difficulty talking about this subject as a lack of trust.
I can wholeheartedly agree with this. I am on the opposite side of this situation, although mine is slightly different... My wife knew about my interest in diapers before we got very serious in our relationship. She was understandably not accepting of it, for some of the reasons ArchieRoni lists above. My reaction was to go along with her and try and purge it from my life. I really loved her, and I didn't want to ruin our otherwise normal relationship with something that is arguably not normal. We dated for just under four years, and we've been married for just over four.
I was fairly successful at getting rid of diapers from my life. I've only bought/worn diapers once since we've been married, and it was when she was on a week-long vacation with her family without me. In my defense, my urges are largely triggered by stress, and I was under a ton of it at the time (I had been along on the vacation with her family but needed to return home to work. My mother-in-law is constantly working against me for various reasons, all pretty unfounded, and it is a very stressful situation for me). I made sure that everything was gone to the dumpster long before she got home, and I felt pretty terrible about it.
See, the thing is, I didn't ask to be this way. I didn't ask to have an attraction (sexual or otherwise) to diapers. So, still to this day, I continue to be at odds with my own brain. I know that "I shouldn't" have this attraction, but I do.
I respect my wife's position, and I don't want to do anything that makes her feel uncomfortable, but I do wish that we could talk about it a little more. Even if she doesn't want to be involved, it kills me that I can't talk about it with my best friend.
I'm not saying you should immediately accept it without any questions or anything like that. It is an uncomfortable topic and you are well within your rights to feel uncomfortable. But, like ArchieRoni said, I think a little compassion and willingness to talk about it goes a long way.
Feel free to reach out to me if you want. We're all different, so I don't know your husband's story, but I can empathize with your situation.
-RD