For what it's worth, I'll throw in my 2 cents.
It seems like there are a lot of people that are into this stuff, but that's just because we surround ourselves with like-minded people. In truth, I think we represent a very thin slice of the population. The chance to get him on-board with this, seem to me to be about as slim as winning the lottery. That doesn't mean it won't happen, and you can give it a shot.
But I'd say you should stop what you're doing right away. If two years go by and then he finds out, then you could say, yes I did that 2 years ago, I realized it was wrong and I stopped, and I'm sorry.
If you keep on doing this until he catches you, then please don't say you're sorry, because that will just make it worse for him. You're not sorry you did it, you're sorry you got caught doing it. There's a big difference.
Say you catch a robber in your house, stealing all your stuff. When you put the 44 mag up to his head, and he says, "I'm sorry." Is he really sorry he's robbing you, or is he really sorry that he's about to meet his maker?"
If you absolutely can't stop doing this, then you should confess to your husband. He deserves the right to be able to decide where it goes from here. If he ends the marriage, oh well. He wasn't the one who rolled the dice, you were.