Originally Posted by Wolfwood
Incidentally, the lie Ciel was referring to involved a guy who marked himself as single on an online dating profile. I think that is a somewhat forgivable sin.
I'd see it as a lie, and a big one at that.
I almost fit your criteria. I had only known there was a word for ethical non-exclusivity for a week or two when I got together with my married boyfriend. His OKCupid profile stated quite clearly that he was married, and while I probably didn't know any better at the time, if he'd hidden that only to tell me later I probably wouldn't have contacted him again.