Hmmm, from what I remember, what I got from the title was that if ML hadn’t caught the boss being engaged that day at the wedding boutique, and if he had not told FL about it, the FL would have not known how she was being cheated and would have lived a life of lies. The boss was gonna send her to Europe, while he would have gotten married in SK but remain in a relationship with the FL flying back and forth, so she would have never known. (At least for a long while).
But I could be way off haha. I do prefer the title “Sunbae, don’t put on that lipstick” so much more.