My wife knows. She's just over 200lb and has known my preferences for a long time. She doesn't want to gain, but she also is pretty content at her current weight, so I don't think she's going to lose either. She teases me with her belly. Her mom is pretty overweight, and we're still young enough that she could get larger with age, but I have mixed feelings about that because I sincerely don't want her health to suffer and I want her to be happy with her body. I once showed her a picture of Boberry and her reaction was sort of "huh! interesting. I've never seen a naked body that big before. enjoy your porn." I've told her I don't want her to be that big (which is true) because I'd be worried about her health, she knows it's just a fantasy.
My best buddy knows also. Aside from that, I'm not shy about mentioning "I like bigger women" if it comes up in conversation with other friends and family, but it rarely does. And I don't think anyone imagines the SSBBW/USSBBW stuff I get off to when I say "bigger women", and I am content with them not knowing. No reason to deal with that conversation and the weirdness that comes with it.
If I was somehow single again, I'd probably go after some larger women just to see what it was like, since I never did when I was younger and had the chance (missed opportunity). 400-500lb. Hard to say if I'd hide it from friends/family or not. I think it would depend a lot on the specific woman and how serious we were. If she had a stable career, pretty face, and good hygiene/fashion (visually I'm thinking about Foxy Roxxie for reference), I'd be fine having her a part of my regular social life. Friends/family might raise their eyebrows but I'm old enough that I wouldn't care as long as she fit my overall vibe/lifestyle. If she fit in less with my lifestyle (more trashy, less fashionable, neurodivergent, maybe more extreme like riding a scooter or something) I'd probably have fun with her temporarily but be uncomfortable introducing her to my social circles long-term.
Super long term though, I wouldn't really want to settle down with anyone north of 350lb. I like my life partner to be able to live life with me - travel, hike, go to concerts, raise a family. I don't want to be a lifelong caretaker just because of a kink. It's why my wife and I work so well together. Great sex, she knows what I'm into, but we can still live a relatively normal life together.