My Wife and I have been together for more than 10 years. I was very upfront about my fetish/desires as I wasn't willing to enter into another relationship with secrets and the eventual issues that come of it. Her wearing diapers for or with me has been a small part of our sex life since the first few months we were together but even then, it has slowly evolved and changed over that time. It took us literally years of careful negotiation, communication and small experiments to arrive where we are today which is a balance that triggers both of our kinks in a very satisfying way but it is not at all what I might have described ten years ago or what I might have fantasied about. That said, I don't think I would actually change things towards what I might have fantasied about.
Ask hard questions and have brutally honest conversations. Understand her motivations, preferences and kinks. Make sure you give and take. Address insecurities and concerns. Understand that communication between men and women is an art. Only through asking hard questions, listening carefully, thinking hard and then verifying my understanding did I unravel her actual desires and discover new ones. Take a small risk once in a while but talk about it after.