When my husband and I first got together, I just assumed he had a very low libido. Later, I assumed his low libido was being exacerbated by job stress and by alcoholism. I had all the right puzzle pieces, but I'd put them in the wrong places. His secret double identity was turning him into an alcoholic and causing him to fail at job after job.
I learned that he had same sex attractions maybe twelve years into the marriage -- after over a decade with no sex. I assumed that since he was so Catholic, he was in denial about his sexuality. And, since we were in pretty much a constant state of crisis financially, I just didn't feel I had the bandwidth to sit him down and ask him what on earth was going on. So I had over two decades of no sex before I found out exactly how active he'd been the whole time.
When I confronted him, he asked me "Did you think I was celibate???" and I acknowledged that yes, that's what I thought (in no small part because he led me to believe it). And he asked with complete incredulity "But how would that have been fair to meeeee???" as if he wasn't even aware of what he'd forced me to endure -- he said it as if it was so obvious, only a complete idiot could fail to see the point. I was absolutely dumbstruck by that remark, and when I pointed out "I never cheated on you" he shrugged and said "I never said you couldn't."
As if he hadn't moved heaven and earth to keep me from knowing what he'd been up to all that time.