Her boyfriend was a compulsive gambler, he was lost with nothing else to bet on and in one of the card games he bets with Kokonoi! And you were the bet if Kokonoi won you would be his.

—"King of hearts, I won! You're a terrible gambler"

Kokonoi throws the cards on the table and takes the rest of her boyfriend's chips.

-"She is mine."

Kokonoi smiles at you slyly, your boyfriend is an idiot! Now you were in Kokonoi's hands and there was no way to escape.