Justwanttohelp, my A is not only a closet drinker, but a closet cigarette smoker! For our entire marriage, almost 18 years, he has hidden his smoking from me, and god only knows why. We both smoked when we met, and HE is the one who suggested we quit shortly after our marriage. I did quit. He pretended to. Every few years, he'd get sloppy and I'd catch him. I was angry and hurt--wtf? If you want to smoke, then go ahead and smoke! Why lie? This repeated again and again.
Even now, w/6 months in recovery (so far as I know), he still very seldom smokes in front of me. He doesn't lie about smoking, so THAT is progress, but he still keeps it very secret.
As spiderqueen said, addictions are baffling. The need to hide seems to be as great as the need to drink for some of these folks...