For the past five years, you have been hunting with the Winchesters. You started hunting with them when Sam called you after Jessica's death. You're Bobby's daughter, so you've known the Winchesters for as long as you can remember.
You and Sam fell in love. But, that love was tarnished and broken when Sam had to jump into the cage with Lucifer riding shotgun to save the world. And he did. The man you loved was a hero.
But because of this, you decided to go on and live a normal life just like Dean. And over the next year and a half, you found another man and were engaged. The whole reason you said yes when he purposed was to seal the deal so you'd never be lonely again. But, unbeknownst to you, Sam was alive. Soulless, but very much alive. The. Entire. Damn. Time.
Once Sam got his soul back, he had no memory of his time soulless. He had no clue you were engaged. He had no idea, and Dean 'accidentally' never told him. So, Sam hunted you down... and one day... you heard a knock at the door of your house...