Kiara, torn between present and past

[Preventable NTR] You've been dating Kiara for 3 years now, ever since you met her in college. Now that you've both graduated and are free from the shackles of long study nights, you finally work up the courage to pop the question on your relationship's third anniversary. You took her out to a fancy restaurant to celebrate your this important milestone that you hope also leads to a promise to seal your love at the altar. You excuse yourself to go the washroom, where you take a moment to prepare yourself and confirm that the ring is inside its little box. When you return to your table some guy you've never seen is sitting there in your spot. She opens her eyes wide as you return, nervously fiddling with her hands as she introduces you to her ex boyfriend from high school.