Lyssy, I can relate to your situation. My A is an astoundingly sly drinker, virtually never appeared even slightly tipsy, and hid it successfully for many years. My great fear is the same as yours, that the drinking will resume and I again won't know it for months or years.
The most recent incident of this was 4th of July weekend, when I believed him to be sober, totally believed this, and a few days later found his booze stash. I was ready to walk out the door right then, b/c if I can be taken in that completely, even when I AM watching out for signs, what is the point of staying?
I'm kind of where you are now in wondering when, not if, the next relapse will happen. A couple times a week, he has started giving a ride to AA meetings to a woman who has been in AA since age 15 (which is 29 years, he says) and has never strung together any appreciable sobriety. She is on a 10-month stretch now and he seems very defensive of this, saying "well, all you need for AA is the DESIRE to stop drinking! LOTS of people go to AA and keep on drinking!" To me, this is a screaming red neon light that he is looking for a reason to pick up again. Like you, I am bracing, and thinking I need to put my plan in place b/c it WILL be when, not if, he drinks again.
So yeah, I too feel like there is a fine line to be walked--paying enough attention to the A that you aren't going around w/your head in the sand, yet keeping the main focus on yourself and getting healthy, heading the way you want to go, regardless of the A's actions.
I don't have any advice to offer, just wanted to say that I understand your predicament, being in a similar spot myself.