In my first relationship, I didn't tell my ex until some months in, and she initially had a bad reaction. I don't really need to get into it other than saying I stayed 4 years too long and got back with her because I bought her "warming up to it" bullshit for that long. In fairness, she did go from absolutely abhorring the idea to being sorta alright with it. But I could have never gotten away with a 24/7 lifestyle. She wouldn't change me. The most I ever got her to do was lay a diaper out for me and she just wasn't ever comfortable with anything else.
Anyway, I was with her 5 years total. One breakup after the first year and a happy six months apart from her and ending up in my one experimental poly relationship where my diapers were again just tolerated but in a much more liberal like "yeah, wear wet diapers in the living room, we don't care! :3" kinda way. No one changed me or anything and actually, upon discovery of my stash, one of my roomies kinda was like "wtf?" but then chilled when I explained it. Neither of them were into ABDL but they were generally kink-aware/positive. Buuut I left for other reasons and ended up back with "warming up to it" girl. For another 4 years.
If you wanna skip all that and read the good part, here it is: here I am now with a fiancée who is wonderful and *loves* my diapers. She loves entertaining my little side and fills our house with toys and diapers. She treats me so unbelievably well. I told her very early on because, after my last lukewarm relationship, I decided that I was going to be upfront about my ABDL identity like, almost first thing once I sense it going somewhere. It worked. I had a few flings with some people who "thought it was cute" and let me ship diapers to their house and stuff... but, ultimately, I met her and she watched me writhe through an uncomfortable explanation just to tell me "Dude, I don't care that you wear diapers. Like at all." and then, disbelieving, I continued to divulge all the aspects of my littleness and puppiness in immense detail and she said, basically, she needed to think about it for a week and do her own research on ABDL etc.
She did exactly that, and then came back and was like, "Yeah, no, you're totally a puppy and I'm kinda down to be your Mommy in a huge way." and the rest is history. I'm diapered (mostly) 24/7 nowadays. I was 24/7 throughout the meat of the pandemic and the only reason I spend a *little* less time in diapers nowadays is because of family crisis reasons that we're both handling. We have an extra head (my brother) in our household temporarily who is underage, so our kink life has had to not be so obvious. I still wear collars and diapers and stuff, but not so obviously. I don't have my diapers and Little stuff just laid out anymore, I don't sit in my messes as much anymore or let my discarded and wrapped-up wet diapers surround the foot of my bed to keep my room smelling like pee and baby powder anymore (it was my fiancée's idea but we both ended up loving it).
I have sippy cups with my name on them, I have onesies and Little clothes, pacifiers (and a locking paci gag!) and hundreds of diapers. I have a growing collection of collars, some I wear in public -- others I wouldn't. All hidden right now due to these exigent circumstances, but we very much live the lifestyle 24/7 in times of peace, and intend to resume once the dust settles on our current situation.
ADVICE: I would say, tell people early. And don't be weird about it. It's all in the delivery. After my 5 year "warming up to it" ex, I resolved to be very open to rejection in my dating life and take the risk of being very upfront. It's all about *how* you tell people. If you frame it like this "weird thing I'm into that you'll probably think I'm crazy for," there's a much higher risk of a potential suitor seeing it as, well, a weird thing you're into that might mean you're a little crazy. A loootttt of people don't know what ABDL is and so their perception of it is *all* up to your delivery. I don't think that's a position a lot of ABDL's appreciate in their relationships and that's why so many people are in ten-year marriages where their wife/husband doesn't know the whole thing or hates it.
I personally wouldn't stay with someone who was disapproving. This is a part of me. If you don't love it, you don't love all of me. That's how I approach it: I wear diapers both because I have a need for them mentally, emotionally, and physically (OAB) but also because I love them and I'm super sensory and they make me feel safe and happy. I'm a puppy because I relate to the young innocence of a puppy more than I feel like a small child (and I'm a furry). It's a very innocent thing and has nothing to do with actual children and I've never been attracted to the actual thought of children in diapers, or diapers as they pertain to children in anyway. My attraction is to *diapers* as an object and *adults* in diapers and mostly the idea of *myself* in diapers. Nor do I see myself as an actual child during relations; I see myself as a submissive adult playing a puppy/child role, power-wise... I have had great luck using this above explanation and expounding on it calmly. I've had a majority successful hitrate trying to get potential s/o's to understand this way. Also, DON'T SETTLE. Don't get with someone, not tell them, or tell them and stay even if they hate it. DON'T. SETTLE. This is a thing people do that baffles me. But even I've done it when I thought that's more than what I deserved! Go into relationships confident about your little/ABDL side and show potential s/o's that this is you EARLY ON and that it is a non-negotiable. "No it can't happen in the background, no it can't happen when you're at work and be put away by the time you come home, no I won't hide my stuff cause the person who apparently loves me thinks this part of me is weird".. It will cost you a few relationships quickly, but you'll soon realize why. The one who says, "Yup, still love you and want all of this," and stays is your soulmate, 10/10 times.
A lot of people complain about ABDL being the bane of their existence and wishing they could extinguish it from their lives. I used to be one of those people until well into my twenties, frankly. I didn't realize until I left my ex that it was my relationship with her that was making me feel largely like I had to "hate" it or feel guilty about it. When she was gone, the guilt was gone. The shame was gone. The feeling like a weirdo was gone. And I radically changed how I approached relationships based on the lifestyle I wanted to live. I 100% believe my ABDL side helped me find true love. I think the more people embrace it and roll with the rejection to get to the good stuff, the more people will realize this side of you is like a filter for the Real Ones when applied correctly. DON'T. SETTLE.