Now, let's do some illogical math first. Assuming that the chance of falling in love with that person is one in seven billion, then the chance of two people falling in love with each other is approximately the square of that number. I don't have a clear idea of how small one is, one-seventh-billionth of a square. In short, it is negligible compared with the probability of any natural or man-made disaster. Since you are in love, it seems to be a matter of course to stay with that person until you grow old. (PS: purely fictional