CoffeeCake, thank you so much for starting this thread. I can empathise, although we were never as kinky as you two.
In our case, it's not a BDSM thing, but he likes me to dress up - stockings, suspender belt, that sort of thing. There's a tinge of dominance to it (i.e., the more restrictive the clothing the better, he enjoys getting to dictate the outfit, etc) but not much. It's certainly something that falls into the realm of kink, in that it isn't part of a larger pattern of behaviour just a fantasy. And he says that while he enjoys good enthusiastic rampant sex without the dress-ups, the dress-ups trigger/release something in his head that's different.
If we don't do it for ages and ages, no matter how much straight sex we have, that desire builds up and up and he gets a bit obsessed. Can't concentrate on work, is horny all the time, that sort of thing. Odd as it seems to me, it really is as if the dress-ups access a different ... hmm, pleasure centre? ... in his brain. So while it sounds pretty vanilla (after all, a lot of men like stockings!) it qualifies as 'kink' to us.
And I've come to understand, over time, that it really isn't as simple as saying 'he should be happy he has a wife who puts out' because it's a wiring thing, and it doesn't seem to me like it's that optional for him. He's said before that he feels guilty for asking, if he could be satisfied with just 'normal' he would, etc.
Similarly, I have a good friend who's heavily into BDSM who describes it as the same as a gender preference for her - she can't make herself like women just by force of will, and she can't make herself vanilla. That was a really powerful way of putting it, that I understood. Sexual preferences are more hardwired for some people than others.
Now in our case, I've made an effort to go along with it even though I find it kind of tedious. It's not degrading, it doesn't require much of me (except for fiddling around with the damn suspender clips!), the sex itself is reliably good.
Your situation is different in that you have to be genuinely into the acts you describe. And that is tricky. After this long a post you'd think I'd have some advice, but I don't. I just wanted to sympathise and tell you that you're not alone, and you sound strong and together and if any marriage can work through this, it'll be yours.
(/novel)