Your heroine is at the airport waiting to pick someone up. She sees an ex-boyfriend at the airport. He’s with his wife (fiance?). She feels a wave of emotion and this sighting of an ex, changes her life.
Who is she picking up at the airport? Her boyfriend? Her mother?
What is the encounter with her ex? Does she say “Hi”? Does she avoid him? Do they have an awkward or a pleasant encounter with him?
How does it change her life? Does she realize what she threw away? Does she realize she’s about to do the same thing with her current boyfriend? Does she have an aha moment that causes her to quit her job and move half way around the country?
Consider describing your heroine first, then determine who your hero is. Is he the ex-boyfriend, the current boyfriend, or someone she has yet to meet? Then work on integrating this scenario into your opening scene.