I know you are getting lots of slaps on the wrist for looking at his papers and I just wanted to say I am sorry you are hurting, and wondering if perhaps there was a degree of testing you going on by leaving those things laying around.
Alcoholics destroy our trust and our ability to trust our instincts, our judgement and ourselves. Reading his private things isn't right-- you already knew that-- but in my al anon group this topic came up a while back and it was shocking to realize how many in the group had done similar things.
It's not okay, or justified, no matter what the A has done, but it is definitely a behavior that is a symptom from having lived with an A.
Just as privacy is sacred, so is truth. When you've been lied to for years and your gut tells you something is not right but the A in front of you tells you you're imagining things, it sure is hard to not be tempted to look for "evidence"... I've been there. Never found anything but have looked and felt very guilty for doing so...