-- chill. not everything has to come up at the front end of a relationship.
I had kinky desires I wasn't going to trot out right away because -- I don't need to play in the deep end of the pool with someone I JUST MET. That doesn't mean that over time it can't happen as the relationship simmers along and catches fire. Don't be so hard on yourself.
If you are a sub newbie, check out "The New Bottoming Book"
and for sake of completeness "The New Topping Book"
. There are other titles for techniques and things but I find those are easy to read for ethics. And even if you don't want to top, reading about topping can help you find a safe top and get your "what do I look for in a dom/top" thing worked out. You don't have to say "yes" just to any top that comes along cuz they call themselves a top. YKWIM?
DO work out your ethics. Knowing YOURSELF and what you wants, needs, soft/hard limits for your "man-woman triad w/ some light BDSM" dance card. When you can be CLEAR, it makes finding a partner that much easier. Then you just have to see if the dance cards can line up or not.
Consider getting involved in your kink community. Dungeons, munches, and so on offer classes, roundtables, socials, support groups in person etc.
Being plus-size is no biggie -- people come in all shapes, colors, and sizes. I was pretty svelte at the start of my adult dating life but illness has tacked on poundage over the years -- and I'm still happy in my rship and haven't had a problem with that. It's how you carry yourself -- truly. There will be people not attracted to plus size -- and that is their right. People get turned on by whatever it is. But there are also people willing to look beyond their initial attraction points. I have a thing for brunettes. So what? I married a blond!
Hang in there.