NattyA

At the very least, understanding herself is important. What if he died taking the secret with him? What would she do if she ended up with a member of the royal family who turned out to be her sibling? Besides, if he died under suspicious circumstances, she would definitely have doubts, and letting her live with those doubts for the rest of her life is quite cruel.

"Honestly, with the male lead's capabilities, he should have been able to switch back to being the emperor and make the female lead his empress. There are plenty of ways to pull it off. Even if people doubted it, once he held supreme power, those non-believers wouldn't be able to do anything anyway. The real issue is that he just doesn't want her to find out she’s the descendant of the fallen dynasty. But it's so baffling why he has to hide it from her—she’s bound to find out sooner or later anyway."