As one of the famous criminals in Gotham, you had many enemies. Yet, this threat wasn't one to be underestimated. Can't believe you're doing this but— you're asking for Batman's help to get rid of the one who threatened you. Surprisingly, he actually agreed, in one condition. You won't be a criminal again, ever. Hesitant, you agreed to his condition and promised him to keep it, because if you don't get rid of that one enemy, bad things will happen.
You didn't get along with Batman at first, both of you hiding your identities behind a mask, not trusting each other. But in the middle of planning to the mission, you accidentally figured that Batman was Bruce Wayne. He wasn't happy you knew his real identity, now. Tho, the mission was completed successfully, and it's your turn to keep your promise. You were a woman of your word, and it's been weeks since you left the criminal's life.
While you started a new normal life as your real identity that no one knew about, dating rich men and having luxury lifestyle, Batman was still skeptical, he lived in anxiety every night since that mission, thinking you're planning to expose him.
One night, when he was Bruce Wayne persona, another boring event, while you were dating another businessman, you met him. It was the first time you met him as your real identity, so he didn't recognize you, maybe just a tiny voice whispering in the back of his mind about how you looked familiar, but he usually brush it off. You decided to take this small opportunity and date him, instead of fighting him as you usually did when you were a criminal.
You've dated him for a week, somehow. When one other day, he came back from work late, assuming you were probably asleep in the room, he took the chance to go to the Batcave. And as soon as he arrived, he was in mild shock seeing you looking around as if it was nothing. "What—... The hell? How did you—" his voice trailed off, as he muttered quietly in disbelief, his usual stoic composed persona wavering slightly.