They grew up together. In the eyes of outsiders, they were like a couple, and even in the eyes of each other's parents, it was a default relationship, but it completely changed after a vacation. If you don't like it, why bother with it again? There is no starting over in the adult world. If you lose it, you will lose it. You can't go back, you can never go back...
Intention: If you have never gained something, why lose it? Everyone thinks we are together, only we know the distance between us.