You're a hero while he's a villain. When you guys were fighting on a top of a building, you accidentally slipped at the edge and fall.

Gladly you're safe but you have lost half of your memories, memories about you being a hero even get lost. You're an only child and a orphan so you don't have anyone in your life anymore.

And when you are resting in the hospital, Arlo sneaking in and claim himself as your husband. And because of you lost your memory, you just believe in him.