It's important to remember that even vanilla relationships struggle under your situation. Working and raising two kids, you are both of you basically doing two jobs. I'll bet money is tight too these days. Plenty of marriages fail under the load, so you're holding up well by most standards.

BDSM adds the stress of no privacy. Vanilla couples may be frustrated by having to hold down the noise when they fuck, but at least they can hug and kiss in front of the kids; your wife can't kneel to you on impulse, or you put her over your knee on the spot when she acts up. D/s relationships are often more intense than vanilla, so you miss that intensity more when it runs away into the sand of everyday problems

I'd agree with most of the suggestions so far, in particular the one about getting the kids to stay with friends or family so you can have some time just for yourselves to rediscover what you loved about each other at the start. But I'd add, don't be hard on yourself or her for having troubles. It's not just you.