What is Love? It is a promise between 2 people. Even if they are far away from each other, Love is still there. The promise is for eternity until one breaks it.
Therefore no matter where you are, how far away from each other, mountains, oceans, valleys apart, if you love someone, you know that your love is for eternity.
If it is love one-sided, it means it's not a promise. there is no 2 people, only 1 sad person, then you know there's this love is not a promise. there would be no eternity.