I'm sure this topic has been beaten to death, but I think it's a really important one that hits at the heart of what causes tons of lurking anxiety and depression in ABDL people. I know for me I've always felt a feeling of defectiveness or differentness about me that has permeated into my personality and sense of well-being. If you feel that there is something so shameful about you that you can't tell anyone about, it'll eat at you and impact your life and relationships, even in seemingly unrelated ways. For most of my 20's I didn't have a girlfriend because I feared what that intimacy would bring out of the shadows, so to speak.
After years of keeping this to myself, I decided to share it with my long-distance girlfriend of 1.5 years. I did it via facebook message, partly because I was at work and partly (maybe mostly) because I was terrified. She was surprised and didn't know how to process the information at first, but she was incredibly supportive and felt that the kink/interest wasn't exactly even all that strange, even if she wasn't into it herself. She reflected back to me that this wasn't something I chose and that she felt sorry that I carried this around with me as a secret, and hoped that telling her released some of my burden (which it did!).
I know how helpful reading other's advice has been on this board, so I wanted to share a couple thoughts/approaches that were key for me in this process. I understand that this is unsolicited advice, and please know that I understand everyone's situation and fetish/lifestyle interests are totally different. I also acknowledge that because I would identify as largely, if not exclusively DL, this may not resonate with every single person. Feel free to offer your thoughts, concerns or corrections to this approach. My hope is that the conversation will be helpful to someone now or down the line.
Again, these are just some approaches that were helpful to me. Some I intuited and others I gained from reading other helpful folks on this and other boards. So, in no particular order, here are some things to think about when introducing your diaper fetish to your partner.
1. If possible, try to contextualize the fetish using language your partner is familiar with or by relating the heart of the kink to something they can wrap their minds around. For me, relating the diaper to a type of lingerie was both honest and easier for her to grasp. It also didn't exclude her from being a subject of my fantasy, which is important to convey if it's possible and honest. She should know that it's not just that diapers get me off, it's that I would be turned on to see HER in a diaper (I understand this may not be the case for everyone, so you may need to be honest depending on your sexual or lifestyle interests). YES… I get turned on by simply wearing a diaper independent of her, but I didn't lead with this information. Control your temptation to dump too much information on your partner. You don't need to reveal the more "extreme" aspects of your kink right away. Let them ask questions.
2. Even if having a partner participate in your fetish with you is an eventual MUST, don't enter the conversation asking anything of your partner except empathy and understanding. I emphasized to my girlfriend straight away that my goal for sharing this information with her was to create greater intimacy between us, NOT to convince her in any way to participate in my fetish. It's tempting, but don't push your partner at all to participate. You can make jokes or bring up the topic playfully over some time, but don't ask them to participate unless they clearly open the door themselves. Let it sit and absorb. The time to decide if their non-participation is a deal breaker is somewhere down the road (maybe a couple weeks to a couple months), but not right away in my opinion.
Trust that if you have the right partner, they will be highly motivated to make sure you are sexually fulfilled, even if that means trying things they are not necessarily into or compromising, if either is possible. However, asking for participation right away is probably asking for too much. Even for a relatively open person, they're still trying to absorb and normalize what you've just told them. They're probably not ready to begin imagining themselves in participation mode. Once they absorb this and normalize it over some time, it becomes less foreign, less weird to them and less scary. Once they reach that point (and this could take weeks or months), THEN I think it's valid to begin feeling them out for participation if that is important to you. However, ideally, don't be in a rush, and be ready to compromise your ideal outcome. It'll be best if it's their idea with no pressure from you.
3. Don't be selfish. If you want someone to be accepting of your kinks, be open and accepting of their kinks or desires as well. Invest just as much time (or more) into your partner sexually that you would hope they'd invest in you.
This strategy not only feels like an honest approach, but has been effective for me so far in laying the foundation for her understanding, and maybe, hopefully, her participation… but on her terms.
For those worried about sharing this information, maybe assess how much shame you carry as a result of hiding it. I can't promise that everyone will be as accepting as my girlfriend, but the potential reward much outweighs the downside of living with anxiety and shame. It feels good to come out and feel accepted. It does wonders for your self-esteem. Also from what I can tell anecdotally from reading tons of threads, a greater number of partners react to this information somewhere on the positive scale rather than on the negative scale. You aren't abnormal. There isn't a normal. You are perfect just the way you are.
Hope this was helpful.