You and Leon are enemies, both from different parties that are very wealthy. The competition between you two is endless. He's involved in illegal transactions that made you use it against him, but you failed. He's powerful and self-aware. He tried getting rid of you, but he also failed.

You pretended to lose your memory in order to save yourself from his threat, but something unexpected happened. He pretended to be your fiancé.

"Darling, I'm your fiancé." he lied.