I had a similar situation, but found a great compromise (with a little luck!):
I was a bedwetter growing up, so she new I had worn diapers. In fact, she knew I enjoyed them, but she thought it was weird and didn't want to participate. I also got the impression that me being diapered was a "turn off" for her. Here's the lucky part. I happened to have a couple of accidents during our first few years of marriage. Sometimes full blown bedwetting, and other times waking up with wet underwear just in time to get to the bathroom. These incidents only happened once every year or 18 months, but she knew they happened. Then last year as we started discussing upgrading our mattress, I realized this was an opportunity to return to diapers. I had already been drinking more water as part of a workout program, so a bedwetting accident was very believable. I had one, we dealt with it, and it was no big deal. I waited about a week and had another. I continued to have random accidents, sometimes after being very tired, and other times after sex. I tried to make it so that there was no one "trigger" that could be the answer. After a while, I mentioned that I think it's just that I'm finally drinking an appropriate amount of water and getting more rest (I had cut back on caffeine too), but that maybe I should see my doctor. I also suggested that maybe I wear "protection" until my appointment so we don't have to deal with wet sheets. She agreed. So I was back into diapers.
The doctor's appointment went well. She just suggested that I'm drinking too much water, and try to limit myself to 60 oz/day. I asked her if it was okay to deal with the problem by wearing diapers like I did when I was 12, and she said that was just fine if I was comfortable with it. I told my wife what she said. Interestingly, I actually only wore them for a month or so, and eventually felt like it was an inconvenience and stopped. (my interest ebbs and flows) I also felt bad that she was turned off by them and didn't want her to be uninterested in having sex with me, so after 7 days of being dry (her rule), I stopped. Not too much time later, I regretted my decision realizing that it might be hard to get back into diapers again if I don't continue wearing them. So I started the infrequent accidents again. This time I started ramping up more quickly, and after a few weeks I had an accident 3 nights in a row. After the 3rd night, she turned to me and said,
"Is there a reason you're not wearing your diapers?" I was hoping she would ask. I told her I thought they were a turnoff for her, but she told me she would rather me be diapered than to have to change the sheets every night. So back into diapers I went, but this time it was her idea. Not long after, we upgraded to the new bed. It's a sleep number bed, so very expensive. She now insists that I'm diapered so I don't ruin the mattress. Especially after sex, she says I don't have a choice. I have to wear a diaper because i sleep so deeply. I'm not allowed to go without until I have 7 dry mornings, but even if that happens again I have a feeling I'll be diapered after sex for the rest of my life.
Moral of the story: even if she's not into it, your relationship will be better if you don't resent her and wish you were with someone you could wear diapers with. You owe it to her to make sure you're both happy so the relationship stays strong. So open your mind, and be willing to take action to get where you want to go. It took me 10 years of marriage before I realized I could do it, but now I'm a happy man.