Yes, it's possible not to know, especially if you've never lived with someone and have fortunate enough never been exposed to the signs of alcohol and drug dependency. And feeling guilt about protecting yourself because you're being battered by manipulation is the most natural thing in the world for codependents -- 99.9% of us here have gone through it. Not sure what you're getting at there.
But anyway, melodymaker, I am so sorry you're going through this pain, and I know exactly how you feel. All I can say is that my prayers go out to you, prayers for strength to continue doing the right thing. Unless you have children, you may want to consider severely limiting the kinds of conversations you have with your husband -- setting some clear boundaries here as to what you will and will not put up with verbally, and keeping your thumb on the hangup buttton, may help you avoid some of the madness.
It's very hard to stand up for one's self to an addict, and at first it feels like your heart is going to explode.
Keep posting and reading and participating here -- you've found a good community for helping stay sane while you work through this.
Hugs,
GL